0001564590-19-044207 | 10-K | XBRL Viewer

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Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Sep. 30, 2019	Nov. 18, 2019	Mar. 31, 2019
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Trading Symbol	CBT
Entity Registrant Name	CABOT CORP
Entity Central Index Key	0000016040
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		56,977,900
Entity Public Float			$ 2,411,701,500
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Interactive Data Current	Yes
Entity File Number	1-5667
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-2271897
Entity Address, Address Line One	Two Seaport Lane
Entity Address, Address Line Two	Suite 1300
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02210
City Area Code	617
Local Phone Number	345-0100
Document Annual Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, $1 par value per share
Security Exchange Name	NYSE

Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net sales and other operating revenues	$ 3,337	$ 3,242	$ 2,717
Cost of sales	2,652	2,470	2,060
Gross profit	685	772	657
Selling and administrative expenses	290	308	262
Research and technical expenses	60	66	57
Specialty Fluids loss on sale and asset impairment charge (Note D)	29
Purification Solutions long-lived assets impairment charge (Note G)		162
Purification Solutions goodwill impairment charge (Note G)		92
Income (loss) from operations	306	144	338
Interest and dividend income	9	10	9
Interest expense	(59)	(54)	(53)
Other income (expense)	(1)	17	5
Income (loss) from continuing operations before income taxes and equity in earnings of affiliated companies	255	117	299
(Provision) benefit for income taxes	(70)	(193)	(33)
Equity in earnings of affiliated companies, net of tax	1	2	7
Net income (loss)	186	(74)	273
Net income (loss) attributable to noncontrolling interests, net of tax of $6, $10 and $6	29	39	25
Net income (loss) attributable to Cabot Corporation	$ 157	$ (113)	$ 248
Weighted-average common shares outstanding:
Basic	58.7	61.7	62.3
Diluted	58.8	61.7	62.7
Earnings per common share:
Basic	$ 2.64	$ (1.85)	$ 3.94
Diluted	$ 2.63	$ (1.85)	$ 3.91

Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net income attributable to noncontrolling interests, tax amount	$ 6	$ 10	$ 6

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 186	$ (74)	$ 273
Other comprehensive income (loss), net of tax
Foreign currency translation adjustment, net of tax (provision) benefit of ($5), $1, and $4	(69)	(64)	25
Unrealized holding gains (losses) arising during the period, net of tax provision of $—, $—, and $—		(1)
Derivatives: net investment hedges
(Gains) losses reclassified to interest expense, net of tax provision (benefit) of $1, $2, and $—	(4)	(3)
(Gains) losses excluded from effectiveness testing and amortized to interest expense, net of tax provision (benefit) of $—, $(1), and $—	1	1
Pension and other postretirement benefit liability adjustments
Pension and other postretirement benefit liability adjustments arising during the period, net of tax	(6)	6	41
Amortization of net loss and prior service credit included in net periodic pension cost, net of tax	1	(1)	2
Specialty Fluids divestiture	(3)
Other comprehensive income (loss)	(80)	(62)	68
Comprehensive income (loss)	106	(136)	341
Net income (loss) attributable to noncontrolling interests, net of tax	29	39	25
Foreign currency translation adjustment attributable to noncontrolling interests, net of tax	(6)	(4)	2
Comprehensive income (loss) attributable to noncontrolling interests	23	35	27
Comprehensive income (loss) attributable to Cabot Corporation	$ 83	$ (171)	$ 314

Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Statement Of Income And Comprehensive Income [Abstract]
Foreign currency translation adjustment, tax (provision) benefit	$ (5)	$ 1	$ 4
(Gains) losses reclassified to interest expense, tax provision (benefit)	$ 1	2
(Gains) losses excluded from effectiveness testing and amortized to interest expense, tax provision (benefit)		$ (1)

Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Current assets:
Cash and cash equivalents	$ 169	$ 175
Accounts and notes receivable, net of reserve for doubtful accounts of $3 and $7	530	637
Inventories	466	511
Prepaid expenses and other current assets	45	63
Total current assets	1,210	1,386
Property, plant and equipment	3,546	3,520
Accumulated depreciation	(2,198)	(2,224)
Net property, plant and equipment	1,348	1,296
Goodwill	90	93
Equity affiliates	39	52
Intangible assets, net	96	98
Assets held for rent		118
Deferred income taxes	163	134
Other assets	58	67
Total assets	3,004	3,244
Current liabilities:
Short-term borrowings	33	249
Accounts payable and accrued liabilities	537	613
Income taxes payable	22	29
Current portion of long-term debt	7	35
Redeemable preferred stock		26
Total current liabilities	599	952
Long-term debt	1,024	719
Deferred income taxes	41	42
Other liabilities	206	252
Commitments and contingencies (Note T)
Preferred stock:
Authorized: 2,000,000 shares of $1 par value Issued and Outstanding: None and none
Common stock:
Authorized: 200,000,000 shares of $1 par value Issued: 57,250,454 and 60,566,375 shares Outstanding 57,080,589 and 60,366,569 shares	57	61
Less cost of 169,865 and 199,806 shares of common treasury stock	(5)	(7)
Retained earnings	1,337	1,417
Accumulated other comprehensive income (loss)	(391)	(317)
Total Cabot Corporation stockholders’ equity	998	1,154
Noncontrolling interests	136	125
Total stockholders’ equity	1,134	1,279
Total liabilities and stockholders’ equity	$ 3,004	$ 3,244

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Statement Of Financial Position [Abstract]
Accounts and notes receivable, reserve for doubtful accounts	$ 3	$ 7
Preferred stock, authorized shares	2,000,000	2,000,000
Preferred stock, par value	$ 1	$ 1
Preferred stock, Issued shares	0	0
Preferred stock, Outstanding shares	0	0
Common stock, authorized shares	200,000,000	200,000,000
Common stock, par value	$ 1	$ 1
Common stock, issued shares	57,250,454	60,566,375
Common stock, outstanding shares	57,080,589	60,366,569
Common treasury stock, shares	169,865	199,806

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Cash Flows from Operating Activities:
Net income (loss)	$ 186	$ (74)	$ 273
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Depreciation and amortization	148	149	155
Specialty Fluids loss on sale and asset impairment charge	29
Impairment of investment in equity affiliate	11
Long-lived asset impairment charge		162
Goodwill impairment charge		92
Deferred tax provision (benefit)	(27)	91	(31)
Employee benefit plan settlement	7
Gain on sale of land		(39)
Gain on sale of investments		(10)
Equity in net income of affiliated companies	(1)	(2)	(7)
Non-cash compensation	11	22	16
Other non-cash (income) expense	(3)	16	(3)
Changes in assets and liabilities:
Accounts and notes receivable	73	(127)	(64)
Inventories	27	(105)	(61)
Prepaid expenses and other current assets	18	(27)	(14)
Accounts payable and accrued liabilities	(75)	122	91
Income taxes payable	(6)	7	(2)
Other liabilities	(37)	12	(16)
Cash dividends received from equity affiliates	2	9	11
Cash provided by operating activities	363	298	348
Cash Flows from Investing Activities:
Additions to property, plant and equipment	(224)	(229)	(147)
Proceeds from sale of business	135
Cash paid for acquisition of business, net of cash acquired of $—, $1 and $—	(3)	(64)
Proceeds from the sale of land		39
Proceeds from sales of investments		11
Other	(2)	(3)	(2)
Cash used in investing activities	(94)	(246)	(149)
Cash Flows from Financing Activities:
Borrowings under financing arrangements	29		1
Repayments under financing arrangements	(29)	(4)	(3)
Increase (decrease) in short-term borrowings, net		(4)	2
Proceeds from (repayments of) issuance of commercial paper, net	(216)	249
Proceeds from long-term debt, net of issuance costs	352	90
Repayments of long-term debt	(75)	(251)	(2)
Repayments of redeemable preferred stock	(25)
Purchases of common stock	(173)	(142)	(61)
Proceeds from sales of common stock	4	22	21
Cash dividends paid to noncontrolling interests	(23)	(21)	(14)
Cash dividends paid to common stockholders	(80)	(80)	(77)
Cash used in financing activities	(236)	(141)	(133)
Effects of exchange rate changes on cash	(39)	(16)	14
Increase (decrease) in cash and cash equivalents	(6)	(105)	80
Cash and cash equivalents at beginning of year	175	280	200
Cash and cash equivalents at end of year	169	175	280
Income taxes paid	99	84	69
Interest paid	$ 47	$ 47	$ 48

Consolidated Statements of Cash Flows (Parenthetical) $ in Millions	12 Months Ended
	Sep. 30, 2018 USD ($)
Statement Of Cash Flows [Abstract]
Cash acquired in acquisition of business	$ 1

Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock, Net of Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total Cabot Corporation Stockholders' Equity [Member]	Noncontrolling Interests [Member]
Beginning Balance at Sep. 30, 2016	$ 1,389	$ 55		$ 1,561	$ (325)	$ 1,291	$ 98
Beginning Balance, Shares at Sep. 30, 2016		62,211
Net income (loss) attributable to Cabot Corporation	248			248		248
Net income (loss) attributable to noncontrolling interests, net of tax of $6, $10 and $6	25						25
Total other comprehensive income (loss)	68				66	66	2
Contributions from noncontrolling interest	4						4
Acquisition of noncontrolling interest			$ (6)			(6)	6
Cash dividends paid/declared to noncontrolling interests	(14)						(14)
Cash dividends paid to common stockholders, per share	(77)			(77)		(77)
Issuance of stock under equity compensation plans	27	$ 2	25			27
Issuance of stock under equity compensation plans, Shares		833
Amortization of share-based compensation	16		16			16
Purchase and retirement of common stock	(61)	$ (1)	(35)	(25)		(61)
Purchase and retirement of common stock, Shares		(1,160)
Ending Balance at Sep. 30, 2017	1,625	$ 56		1,707	(259)	1,504	121
Ending Balance, Shares at Sep. 30, 2017		61,884
Net income (loss) attributable to Cabot Corporation	(113)			(113)		(113)
Net income (loss) attributable to noncontrolling interests, net of tax of $6, $10 and $6	39						39
Total other comprehensive income (loss)	(62)				(58)	(58)	(4)
Acquisition of noncontrolling interest			(1)			(1)	1
Cash dividends paid/declared to noncontrolling interests	(32)						(32)
Cash dividends paid to common stockholders, per share	(80)			(80)		(80)
Issuance of stock under equity compensation plans	22		22			22
Issuance of stock under equity compensation plans, Shares		733
Amortization of share-based compensation	22		22			22
Purchase and retirement of common stock	(142)	$ (2)	(43)	(97)		(142)
Purchase and retirement of common stock, Shares		(2,250)
Ending Balance at Sep. 30, 2018	1,279	$ 54		1,417	(317)	1,154	125
Ending Balance, Shares at Sep. 30, 2018		60,367
Net income (loss) attributable to Cabot Corporation	157			157		157
Net income (loss) attributable to noncontrolling interests, net of tax of $6, $10 and $6	29						29
Total other comprehensive income (loss)	(80)				(74)	(74)	(6)
Acquisition of noncontrolling interest			(1)			(1)	1
Cash dividends paid/declared to noncontrolling interests	(13)						(13)
Cash dividends paid to common stockholders, per share	(80)			(80)		(80)
Issuance of stock under equity compensation plans	4	$ 2	2			4
Issuance of stock under equity compensation plans, Shares		483
Amortization of share-based compensation	11		11			11
Purchase and retirement of common stock	(173)	$ (4)	$ (12)	(157)		(173)
Purchase and retirement of common stock, Shares		(3,769)
Ending Balance at Sep. 30, 2019	$ 1,134	$ 52		$ 1,337	$ (391)	$ 998	$ 136
Ending Balance, Shares at Sep. 30, 2019		57,081

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Statement Of Stockholders Equity [Abstract]
Cash dividends paid, per share	$ 1.36	$ 1.29	$ 1.23

Significant Accounting Policies

12 Months Ended

Sep. 30, 2019

Accounting Policies [Abstract]

Significant Accounting Policies

Note A. Significant Accounting Policies

The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S.”). The significant accounting policies of Cabot Corporation (“Cabot” or “the Company”) are described below.

Unless otherwise indicated, all disclosures and amounts in the Notes to the Consolidated Financial Statements relate to the Company’s continuing operations.

Effective October 1, 2018, the Company adopted the new revenue recognition standard that amended the pre-existing accounting standard for revenue recognition. The Company used a modified retrospective approach, which is discussed in further detail in Note B.

Effective October 1, 2018, the Company adopted the new pension standard that amended the requirements on the presentation of net periodic pension and postretirement benefit costs. The Company used a retrospective transition method to reclassify net periodic benefit cost, other than the service component, from Cost of sales, Selling and administrative expenses and Research and technical expenses to Other income (expense) in the Consolidated Statements of Operations for the prior periods presented, which is discussed in further detail in Note B.

Effective October 1, 2018, the Company realigned its business reporting structure under the Performance Chemicals segment and now combines its specialty carbons, fumed metal oxides and aerogel product lines into the Performance Additives business, and its specialty compounds and inkjet product lines into the Formulated Solutions business. Prior period Performance Chemicals segment revenue results have been recast to reflect the realignment.

In January 2019, the Company entered into an agreement to sell its Specialty Fluids business to Sinomine (Hong Kong) Rare Metals Resources Co. Limited, a wholly owned subsidiary of Sinomine Resource Group Co., Ltd. (“Sinomine”). The sale of the Specialty Fluids business closed in June 2019 and does not meet the criteria to be reported as a discontinued operation. Therefore, prior periods’ consolidated financial statements and disclosures have not been recast. Refer to Note D for further details regarding the sale of the Specialty Fluids business.

Principles of Consolidation

The consolidated financial statements include the accounts of Cabot and its wholly-owned subsidiaries and majority-owned and controlled U.S. and non-U.S. subsidiaries. Additionally, Cabot considers consolidation of entities over which control is achieved through means other than voting rights, of which there were none in the periods presented. Intercompany transactions have been eliminated in consolidation.

Cash and Cash Equivalents

Cash equivalents include all highly liquid investments with a maturity of three months or less at date of acquisition. Cabot continually assesses the liquidity of cash equivalents and, as of September 30, 2019, has determined that they are readily convertible to cash.

Inventories

Inventories are stated at the lower of cost or net realizable value. The cost of Specialty Fluids inventories that were classified as assets held for rent was determined using the average cost method. The cost of all other inventories is determined using the first-in, first-out method.

Cabot periodically reviews inventory for both potential obsolescence and potential declines in anticipated selling prices. In this review, the Company makes assumptions about the future demand for and market value of the inventory, and based on these assumptions estimates the amount of any obsolete, unmarketable, slow moving, or overvalued inventory. Cabot writes down the value of these inventories by an amount equal to the difference between the cost of the inventory and its estimated net realizable value.

Investments

The Company has investments in equity affiliates and marketable securities. As circumstances warrant, all investments are subject to periodic impairment reviews. Unless consolidation is required, investments in equity affiliates, where Cabot generally owns between 20% and 50% of the affiliate, are accounted for using the equity method. Cabot records its share of the equity affiliate’s results of operations based on its percentage of ownership of the affiliate. Dividends declared from equity affiliates are a return on investment and are recorded as a reduction to the equity investment value. In the second quarter of fiscal 2019, the Company recorded an impairment charge of $11 million related to its Venezuelan equity investment, which is included in Other income (expense) within the Consolidated Statements of Operations. Refer to Note M for details related to the impairment charge. At September 30, 2019 and 2018, Cabot had equity affiliate investments of $39 million and $52 million, respectively. Dividends declared and received from these investments were $4 million, $9 million and $11 million in fiscal 2019, 2018 and 2017, respectively.

Intangible Assets and Goodwill Impairment

The Company records tangible and intangible assets acquired and liabilities assumed in business combinations under the acquisition method of accounting. Amounts paid for an acquisition are allocated to the assets acquired and liabilities assumed based on their fair values at the date of acquisition. The Company uses assumptions and estimates in determining the fair value of assets acquired and liabilities assumed in a business combination. The determination of the fair value of intangible assets requires the use of significant judgment with regard to assumptions used in the valuation model. The Company estimates the fair value of identifiable acquisition-related intangible assets principally based on projections of cash flows that will arise from these assets. The projected cash flows are discounted to determine the fair value of the assets at the dates of acquisition.

Definite-lived intangible assets, which are comprised of trademarks, customer relationships and developed technologies, are amortized over their estimated useful lives and are reviewed for impairment when indication of potential impairment exists, such as a significant reduction in cash flows associated with the assets.

Goodwill is comprised of the purchase price of business acquisitions in excess of the fair value assigned to the net tangible and identifiable intangible assets acquired. Goodwill is not amortized and is subject to impairment testing annually, or when events or changes in the business environment indicate that the carrying value of the reporting unit may exceed its fair value.

Historically, the annual goodwill impairment test was performed as of May 31. During the fourth quarter of fiscal 2019, the Company changed the date of the impairment test to August 31. This date is preferred as it better aligns with the Company’s planning process, which produces a significant input to the testing, and it did not result in a material change to the Company’s consolidated financial statements.

A reporting unit, for the purpose of the impairment test, is at or below the operating segment level, and constitutes a business for which discrete financial information is available and regularly reviewed by segment management. Reinforcement Materials, and the fumed metal oxides and specialty compounds product lines within Performance Chemicals, which are considered separate reporting units, carry the Company’s goodwill balances as of September 30, 2019.

For the purpose of the goodwill impairment test, the Company first assesses qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If an initial qualitative assessment identifies that it is more likely than not that the carrying value of a reporting unit exceeds its estimated fair value, an additional quantitative evaluation is performed. Alternatively, the Company may elect to proceed directly to the quantitative goodwill impairment test. If based on the quantitative evaluation the fair value of the reporting unit is less than its carrying amount, a goodwill impairment loss would result. The goodwill impairment loss would be the amount by which the carrying value of the reporting unit, including goodwill, exceeds its fair value, limited to the total amount of goodwill allocated to that reporting unit. The fair value of a reporting unit is based on discounted estimated future cash flows. The fair value is also benchmarked against the value calculated from a market approach using the guideline public companies method. The assumptions used to estimate fair value include management’s best estimates of future growth rates, operating cash flows, capital expenditures and discount rates over an estimate of the remaining operating period at the reporting unit level. Based on the Company’s most recent annual goodwill impairment test performed as of August 31, 2019, the fair values of the Reinforcement Materials, Fumed Metal Oxides and Specialty Compounds reporting units were substantially in excess of their carrying values. Refer to Note G for details on the Purification Solutions goodwill impairment test and the resulting impairment charge recorded in the second quarter of fiscal 2018.

Long-lived Assets Impairment

The Company’s long-lived assets primarily include property, plant and equipment, intangible assets, long-term investments and assets held for rent. The carrying values of long-lived assets are reviewed for impairment whenever events or changes in business circumstances indicate that the carrying amount of an asset may not be recoverable.

To test for impairment of assets, the Company generally uses a probability-weighted estimate of the future undiscounted net cash flows of the assets over their remaining lives to determine if the value of the asset is recoverable. Long-lived assets are grouped with other assets and liabilities at the lowest level for which independent identifiable cash flows are determinable.

An asset impairment is recognized when the carrying value of the asset is not recoverable based on the analysis described above, in which case the asset is written down to its fair value. If the asset does not have a readily determinable market value, a discounted cash flow model may be used to determine the fair value of the asset. In circumstances when an asset does not have separate identifiable cash flows, an impairment charge is recorded when the Company no longer intends to use the asset. Refer to Note G regarding the results of the recoverability test performed on the long-lived assets of the Purification Solutions segment and the resulting impairment charge recorded in the second quarter of fiscal 2018.

The Company continues to consider strategic options for its Purification Solutions business. Depending on the actions taken, there could be a negative impact on the fair value of the Purification Solutions reporting unit, which may lead to further impairment.

Property, Plant and Equipment

Property, plant and equipment are recorded at cost. Depreciation of property, plant and equipment is calculated using the straight-line method over the estimated useful lives of the related assets. The depreciable lives for buildings, machinery and equipment, and other fixed assets are generally between twenty and twenty-five years, ten and twenty-five years, and three and twenty-five years, respectively. The cost and accumulated depreciation for property, plant and equipment sold, retired, or otherwise disposed of are removed from the Consolidated Balance Sheets and resulting gains or losses are included in earnings in the Consolidated Statements of Operations. Expenditures for repairs and maintenance are charged to expenses as incurred. Expenditures for major renewals and betterments, which significantly extend the useful lives of existing plant and equipment, are capitalized and depreciated.

Capital expenditures for property, plant and equipment included in Accounts payable and accrued liabilities were approximately $23 million, $29 million and $7 million for the years ended September 30, 2019, 2018, and 2017, respectively.

Cabot capitalizes interest costs when they are part of the historical cost of acquiring and constructing certain assets that require a period of time to prepare for their intended use. During fiscal 2019, 2018 and 2017, Cabot capitalized $4 million, $2 million and $1 million of interest costs, respectively. These amounts are amortized over the lives of the related assets when they are placed in service.

Asset Retirement Obligations

Cabot estimates incremental costs for special handling, removal and disposal of materials that may or will give rise to conditional asset retirement obligations (“ARO”) and then discounts the expected costs back to the current year using a credit adjusted risk free rate. Cabot recognizes ARO liabilities and costs when the timing and/or settlement can be reasonably estimated. In certain instances, Cabot has not recorded a reserve for AROs because of the indefinite life of certain assets. The ARO reserves were $26 million and $28 million at September 30, 2019 and 2018, respectively, and are included in Accounts payable and accrued liabilities and Other liabilities on the Consolidated Balance Sheets.

Foreign Currency Translation

The functional currency of the majority of Cabot’s foreign subsidiaries is the local currency in which the subsidiary operates. Assets and liabilities of foreign subsidiaries are translated into U.S. dollars at exchange rates in effect at the balance sheet dates. Income and expense items are translated at average monthly exchange rates during the year. Unrealized currency translation adjustments are included as a separate component of Accumulated other comprehensive income (loss) (“AOCI”) within stockholders’ equity.

Realized and unrealized foreign currency gains and losses arising from transactions denominated in currencies other than the subsidiary’s functional currency are reflected in earnings with the exception of (i) intercompany transactions considered to be of a long-term investment nature; (ii) income taxes upon future repatriation of unremitted earnings from non-U.S. subsidiaries that are not indefinitely reinvested; and (iii) foreign currency borrowings designated as net investment hedges. Gains or losses arising from these transactions are included as a component of Other comprehensive income (loss). In fiscal 2019, 2018 and 2017, net foreign currency transaction gains of less than $1 million, and losses of $4 million, and $4 million, respectively, are included in Other income (expense) in the Consolidated Statements of Operations.

Beginning July 1, 2018, the Argentina economy was determined to be highly inflationary. As a result, the functional currency of the Company’s Argentina subsidiary was changed to the U.S. dollar, Cabot’s reporting currency, which is discussed in Note M.

Share Repurchases

Periodically, Cabot repurchases shares of the Company’s common stock in the open market or in privately negotiated transactions under the authorization approved by the Board of Directors as discussed in Item 5 under the heading “Issuer Purchases of Equity Securities”. The Company retires the repurchased shares and records the excess of the purchase price over par value to additional paid-in capital (“APIC”) until such amount is reduced to zero and then charges the remainder against retained earnings.

Financial Instruments

Cabot’s financial instruments consist primarily of cash and cash equivalents, accounts and notes receivable, investments, accounts payable and accrued liabilities, short-term and long-term debt, and derivative instruments. The carrying values of Cabot’s financial instruments approximate fair value with the exception of fixed rate long-term debt, which is recorded at amortized cost. The fair values of the Company’s financial instruments are based on quoted market prices, if such prices are available. In situations where quoted market prices are not available, the Company relies on valuation models to derive fair value. Such valuation takes into account the ability of the financial counterparty to perform and the Company’s own credit risk.

Cabot uses derivative financial instruments primarily for purposes of hedging the exposures to fluctuations in foreign currency exchange rates, which exist as part of its on-going business operations. Cabot does not enter into derivative contracts for speculative purposes, nor does it hold or issue any derivative contracts for trading purposes. All derivatives are recognized on the Consolidated Balance Sheets at fair value. Where Cabot has a legal right to offset derivative settlements under a master netting agreement with a counterparty, derivatives with that counterparty are presented on a net basis. The changes in the fair value of derivatives are recorded in either earnings or AOCI, depending on whether or not the instrument is designated as part of a hedge transaction and, if designated as part of a hedge transaction, the type of hedge transaction. The gains or losses on derivative instruments reported in AOCI are reclassified to earnings in the period in which earnings are affected by the underlying hedged item. The ineffective portion of all hedges is recognized in earnings during the period in which the ineffectiveness occurs.

In accordance with Cabot’s risk management strategy, the Company may enter into certain derivative instruments that may not be designated as hedges for hedge accounting purposes. Although these derivatives are not designated as hedges, the Company believes that such instruments are closely correlated with the underlying exposure, thus managing the associated risk. The Company records in earnings the gains or losses from changes in the fair value of derivative instruments that are not designated as hedges. Cash movements associated with these instruments are presented in the Consolidated Statements of Cash Flows as Cash Flows from Operating Activities because the derivatives are designed to mitigate risk to the Company’s cash flow from operations. The cash flows related to the principal amount of outstanding debt instruments are presented in the Cash Flows from Financing Activities section of the Consolidated Statements of Cash Flows.

Revenue Recognition

Cabot recognizes revenue when its customers obtain control of promised goods or services. The revenue recognized is the amount of consideration which the Company expects to receive in exchange for those goods or services. The Company’s contracts with customers are generally for products only and do not include other performance obligations. Generally, Cabot considers purchase orders, which in some cases are governed by master supply agreements, to be contracts with customers. The transaction price as specified on the purchase order or sales contract is considered the standalone selling price for each distinct product. To determine the transaction price at the time when revenue is recognized, the Company evaluates whether the price is subject to adjustments, such as for returns, discounts or volume rebates, which are stated in the customer contract, to determine the net consideration to which the Company expects to be entitled. Revenue from product sales is recognized based on a point in time model when control of the product is transferred to the customer, which typically occurs upon shipment or delivery of the product to the customer and title, risk and rewards of ownership have passed to the customer. The Company has an immaterial amount of revenue that is recognized over time. Payment terms typically range from zero to ninety days.

Shipping and handling activities that occur after the transfer of control to the customer are billed to customers and are recorded as sales revenue, as the Company considers these to be fulfillment costs. Shipping and handling costs are expensed in the period incurred and included in Cost of sales within the Consolidated Statement of Operations. Taxes collected on sales to customers are excluded from the transaction price.

The Company generally provides a warranty that its products will substantially conform to the identified specifications. The Company’s liability typically is limited to either a credit equal to the purchase price or replacement of the non-conforming product. Returns under warranty have historically been immaterial.

Revenue in the Specialty Fluids segment arose primarily from the rental of cesium formate. This revenue was recognized throughout the rental period based on the contracted rental terms. Customers were also billed and revenue was recognized, typically at the end of the rental period, for cesium formate product that was not returned. The Company also generated revenues from cesium formate sold outside of the rental process and from the sale of fine cesium chemicals. This revenue was recognized when control of the product transferred to the customer, which was typically upon delivery of the product.

The Company does not have contract assets or liabilities that are material.

As permitted by the revenue recognition standard, Revenue from Contracts with Customers, issued by the Financial Accounting Standards Board (“FASB”), when the period of time between the transfer of control of the goods and the time the customer pays for the goods is one year or less, the Company does not consider there to be a significant financing component associated with the contract.

Cost of Sales

Cost of sales consists of the cost of raw and packaging materials, direct manufacturing costs, depreciation, internal transfer costs, inspection costs, inbound and outbound freight and shipping and handling costs, plant purchasing and receiving costs and other overhead expenses necessary to manufacture the products.

Accounts and Notes Receivable

Trade receivables are recorded at the invoiced amount and generally do not bear interest. Trade receivables in China may at certain times be settled with the receipt of bank issued non-interest bearing notes. These notes totaled 30 million Chinese Renminbi (“RMB”) ($4 million) and 32 million RMB ($5 million) as of September 30, 2019 and 2018, respectively, and are included in Accounts and notes receivable on the Company’s Consolidated Balance Sheets. Cabot periodically sells a portion of these bank notes and other customer receivables at a discount and such sales are accounted for as asset sales. The Company does not have any continuing involvement with these notes or other customer receivables after the sale. The difference between the proceeds from the sale and the carrying value of these assets is recognized as a loss on the sale of receivables and is included in Other income (expense) in the accompanying Consolidated Statements of Operations. During fiscal 2019, 2018 and 2017, the Company recorded charges of $3 million, $3 million, and $2 million, respectively, for the sale of these assets.

Cabot maintains allowances for doubtful accounts based on an assessment of the collectability of specific customer accounts, the aging of accounts receivable and other economic information on both a historical and prospective basis. Customer account balances are charged against the allowance when it is probable the receivable will not be recovered. There were no material changes in the allowance for any of the years presented. There is no material off-balance sheet credit exposure related to customer receivable balances.

Stock-based Compensation

Cabot recognizes compensation expense for stock-based awards granted to employees using the fair value method. Under the fair value recognition provisions, stock-based compensation cost is measured at the grant date based on the fair value of the award, and is recognized as expense over the service period, which generally represents the vesting period, and includes an estimate of what level of performance the Company will achieve for Cabot’s performance-based stock awards. Cabot calculates the fair value of its stock options using the Black-Scholes option pricing model. The fair value of restricted stock units is determined using the closing price of Cabot stock on the day of the grant. The Company recognizes forfeitures as they occur.

Selling and Administrative Expenses

Selling and administrative expenses consist of salaries and fringe benefits of sales and office personnel, general office expenses and other expenses not directly related to manufacturing operations.

Research and Technical Expenses

Research and technical expenses include salaries, equipment and material expenditures, and contractor fees and are expensed as incurred.

Income Taxes

Deferred income taxes are determined based on the estimated future tax effects of differences between financial statement carrying amounts and the tax bases of existing assets and liabilities. Deferred tax assets are recognized to the extent that realization of those assets is considered to be more likely than not.

A valuation allowance is established for deferred taxes when it is more likely than not that all or a portion of the deferred tax assets will not be realized. Provisions are made for the U.S. income tax liability and additional non-U.S. taxes on the undistributed earnings of non-U.S. subsidiaries, except for amounts Cabot has designated to be indefinitely reinvested.

Cabot records benefits for uncertain tax positions based on an assessment of whether the position is more likely than not to be sustained by the taxing authorities. If this threshold is not met, no tax benefit of the uncertain tax position is recognized. If the threshold is met, the tax benefit that is recognized is the largest amount that is greater than 50% likely of being realized upon ultimate settlement. This analysis presumes the taxing authorities’ full knowledge of the positions taken and all relevant facts, but does not consider the time value of money. The Company also accrues for interest and penalties on its uncertain tax positions and includes such charges in its income tax provision in the Consolidated Statements of Operations.

Environmental Costs

Cabot accrues environmental costs when it is probable that a liability has been incurred and the amount can be reasonably estimated. When a single liability amount cannot be reasonably estimated, but a range can be reasonably estimated, Cabot accrues the amount that reflects the best estimate within that range or the low end of the range if no estimate within the range is better. The amount accrued reflects Cabot’s assumptions about remediation requirements at the contaminated site, the nature of the remedy, the outcome of discussions with regulatory agencies and other potentially responsible parties at multi-party sites, and the number and financial viability of other potentially responsible parties. Cabot does not reduce its estimated liability for possible recoveries from insurance carriers. Proceeds from insurance carriers are recorded when realized by either the receipt of cash or a contractual agreement.

Use of Estimates

The preparation of consolidated financial statements in conformity with generally accepted accounting principles in the U.S. requires management to make certain estimates and assumptions that affect the reported amount of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reported period. Actual results could differ from those estimates.

Recent Accounting Pronouncements

12 Months Ended

Sep. 30, 2019

Accounting Changes And Error Corrections [Abstract]

Recent Accounting Pronouncements

Note B. Recent Accounting Pronouncements

Recently Adopted Accounting Standards

In May 2014, the FASB issued a new standard, Revenue from Contracts with Customers, that amended the existing accounting standards for revenue recognition. The standard requires entities to recognize revenue when they transfer promised goods or services to customers in an amount that reflects the consideration the entity expects to be entitled to in exchange for those goods or services. The Company adopted this standard on October 1, 2018 and applied a modified retrospective approach. The comparative information has not been restated and continues to be reported under the accounting standards in effect during those periods.

The adoption of this standard did not have an impact on how the Company recognizes revenue. As such, an adjustment to opening retained earnings was not required. The Company implemented the updates that were necessary to its revenue recognition policy, internal controls, processes and financial statement disclosures as part of this adoption. The updated disclosures are reflected under the heading “Revenue Recognition” within Note A and the Company’s disaggregated revenue is reflected within Note U.

In addition, as part of an assessment performed in connection with adopting this standard, the Company reviewed its classification of by-product sales, which consist of sales generated from the production of steam or electricity from the Company's energy centers primarily from its carbon black manufacturing sites and sales of hydrochloric acid generated from the production of fumed silica. Historically, the Company presented by-product sales as a reduction of Cost of sales within the Consolidated Statement of Operations. However, upon further evaluation of these sales in connection with the implementation of this standard, the Company determined that it is appropriate to present by-product sales as Net sales and other operating revenues. Effective October 1, 2018, these sales have been included within Net sales and other operating revenues in the Consolidated Statement of Operations. This change did not result in a cumulative adjustment to opening retained earnings as it is a classification change within the Consolidated Statement of Operations. If the Company had continued to classify by-product sales within Cost of sales, there would have been a decrease to Net sales and other operating revenues and Cost of sales of $76 million for the year ended September 30, 2019.

In August 2016, the FASB issued final amendments to clarify how entities should classify certain cash receipts and cash payments on the statement of cash flows, such as distributions received from equity method investees, proceeds from the settlement of insurance claims, and proceeds from the settlement of corporate-owned life insurance policies. The Company adopted this standard on October 1, 2018. The adoption of this standard did not have a material impact to the Company’s consolidated financial statements.

In March 2017, the FASB issued a new standard that amends the requirements on the presentation of net periodic pension and postretirement benefit costs. The new standard requires the service cost component to be presented with other employee compensation costs. The other components will be reported separately outside of operations. Only the service cost component will be eligible for capitalization. Entities are required to use a retrospective transition method to adopt the requirement for separate income statement presentation of the service cost and other components, and a prospective transition method to adopt the requirement to limit the capitalization of benefit cost to the service component. The Company adopted the standard on October 1, 2018 and used a retrospective transition method to reclassify net periodic benefit cost, other than the service component, from Cost of sales, Selling and administrative expenses and Research and technical expenses to Other income (expense) in the Consolidated Statements of Operations for the prior periods presented. In accordance with the standard, the Company utilized prior period footnote disclosures as a practical expedient to apply these retrospective presentations, which is shown in the table below:

Consolidated Statements of Operations	Years Ended September 30
	2018							2017
	As Originally Reported		Effect of Change			As Adjusted		As Originally Reported			Effect of Change			As Adjusted

Cost of sales	$	2,461	$	9		$	2,470	$	2,054		$	6		$	2,060
Gross profit	$	781	$	(9	)	$	772	$	663		$	(6	)	$	657
Selling and administrative expenses	$	305	$	3		$	308	$	260		$	2		$	262
Research and technical expenses	$	66	$	—		$	66	$	56		$	1		$	57
Income (loss) from operations	$	156	$	(12	)	$	144	$	347		$	(9	)	$	338
Other income (expense)	$	5	$	12		$	17	$	(4	)	$	9		$	5

In August 2018, the FASB issued a new standard to align the requirements for capitalizing implementation costs incurred in a cloud computing arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software. The updated guidance also requires an entity to expense the capitalized implementation costs of a cloud computing arrangement that is a service contract over the term of the arrangement and includes expanded disclosure requirements for such costs. The Company adopted this standard prospectively on January 1, 2019. The adoption of this standard did not have a material impact to the Company’s consolidated financial statements.

Recently Issued Accounting Pronouncements

In February 2016, the FASB issued a new standard for the accounting for leases. This new standard requires lessees to recognize assets and liabilities for most leases, but recognize expenses on their income statements in a manner that is similar to the current accounting treatment for leases. The standard is applicable for fiscal years beginning after December 15, 2018 and for interim periods within those years, and early adoption is permitted. The Company adopted the standard on October 1, 2019 using the modified retrospective optional transition method, in which case prior periods presented will not be restated. The Company elected the package of practical expedients, which, among other things, permits the Company to not reassess the identification, classification and initial direct costs of leases commencing before the October 1, 2019 effective date and not include short-term leases on the balance sheet. The Company’s implementation team completed analyzing the current portfolio of leases and is currently developing its lease disclosures beginning with quarterly reporting for the period ended December 31, 2019. As of the date of implementation, October 1, 2019, the impact of the adoption was estimated to result in recognition of a right of use asset and lease payable obligation on the Company’s consolidated balance sheet of approximately $100 million to $120 million. The implementation team was responsible for evaluating and designing the necessary changes to the Company’s business processes, lease policies, systems and internal controls to support recognition and disclosure under the new guidance.

In June 2016, the FASB issued a new standard on measurement of credit losses. The standard introduces a new "expected loss" impairment model that applies to most financial assets measured at amortized cost and certain other instruments, including trade and other receivables and other financial assets. Entities are required to estimate expected credit losses over the life of financial assets and record an allowance against the assets’ amortized cost basis to present them at the amount expected to be collected. The new standard is effective for fiscal years beginning after December 15, 2019 and early adoption is permitted. The Company is evaluating this standard and the timing of its adoption. The Company does not expect the adoption of this standard to materially impact the Company’s consolidated financial statements.

In February 2018, the FASB issued a new standard that allows entities to reclassify from AOCI to Retained earnings stranded tax effects resulting from changes made as a result of the Tax Cuts and Jobs Act of 2017 (the “Act”). The amendments in this new standard also require certain disclosures about stranded tax effects. The new standard is effective for all entities for fiscal years beginning after December 15, 2018, including interim periods within those years, and early adoption is permitted. The Company adopted the standard on October 1, 2019. The Company does not expect the adoption of this standard to materially impact the Company’s consolidated financial statements.

Acquisitions

12 Months Ended

Sep. 30, 2019

Business Combinations [Abstract]

Acquisitions

Note C. Acquisitions

Tech Blend

In November 2017, the Company acquired Tech Blend, a North American producer of black masterbatches, for a purchase price of $65 million, paid in cash. The purchase price was subject to a working capital adjustment, which was immaterial. The operating results of the business are included in the Company’s Performance Chemicals segment. The acquisition extends the Company’s global footprint in black masterbatch and compounds and provides a platform to serve global customers and grow in conductive formulations.

NSCC Carbon (Jiangsu) Co. Ltd

In September 2018, the Company acquired NSCC Carbon, a carbon black manufacturing facility in Pizhou, Jiangsu Province, China for a purchase price of $8 million. The purchase price conditions were satisfied in September 2019 and the purchase price is expected to be paid in the first quarter of fiscal 2020. The accrual for this payment is currently recorded within Accounts payable and accrued liabilities on the Consolidated Balance Sheets. The Company plans to modify this facility to produce specialty carbons and therefore the plant is temporarily mothballed. The modifications are expected to be completed, and production is expected to commence, in 2021. During the fiscal year ended 2019 the Company has incurred $4 million of transition-related costs associated with this acquisition.

Other Acquisition

In June 2019, the Company acquired certain intangible assets from a leading masterbatch producer in Asia. The total purchase price of $3 million was allocated to customer relationships and is presented in Intangible assets, net on the Consolidated Balance Sheets. The acquisition extends the Company’s global footprint in black masterbatch.

Sale of the Specialty Fluids Business

12 Months Ended

Sep. 30, 2019

Discontinued Operations And Disposal Groups [Abstract]

Sale of the Specialty Fluids Business

Note D. Sale of the Specialty Fluids Business

In June 2019, the Company completed the sale of its Specialty Fluids business, an operating segment of the Company, to Sinomine for total proceeds of $133 million, net of $2 million cash transferred, subject to customary post-closing adjustments that are not expected to be material.

The Company recognized a pre-tax loss on the sale of the Specialty Fluids business of $9 million in fiscal 2019 and a $20 million impairment charge during the second quarter of fiscal 2019. The sale of the Specialty Fluids business does not meet the criteria to be reported as a discontinued operation as it does not constitute a significant strategic business shift for the Company, and has no major effect on operations.

As part of the sale, the Company may receive additional cash royalties of up to $5 million for lithium products, payable over a ten-year period.

Inventories

12 Months Ended

Sep. 30, 2019

Inventory Disclosure [Abstract]

Inventories

Note E. Inventories

Inventories, net of obsolete, unmarketable and slow moving reserves, are as follows:

	September 30
	2019		2018
	(In millions)
Raw materials	$	107	$	129
Work in process		—		3
Finished goods		305		329
Other		54		50
Total	$	466	$	511

Other inventory is comprised of certain spare parts and supplies.

Cabot periodically reviews inventory for both obsolescence and loss of value. In this review, Cabot makes assumptions about the future demand for and market value of the inventory and, based on these assumptions, estimates the amount of obsolete, unmarketable or slow moving inventory. At September 30, 2019 and 2018, total inventory reserves were $29 million and $38 million, respectively. During fiscal year 2018, the Company recorded a lower of cost or market charge in the amount of $13 million related to its Purification Solutions inventory held at several sites in North America and Europe.

Property, Plant and Equipment

12 Months Ended

Sep. 30, 2019

Property Plant And Equipment [Abstract]

Property, Plant and Equipment

Note F. Property, Plant and Equipment

Property, plant and equipment consists of the following:

	September 30
	2019			2018
	(In millions)
Land and land improvements	$	144		$	142
Buildings		524			514
Machinery and equipment		2,369			2,373
Other		247			249
Construction in progress		262			242
Total property, plant and equipment		3,546			3,520
Less: Accumulated depreciation		(2,198	)		(2,224	)
Net property, plant and equipment	$	1,348		$	1,296

Depreciation expense was $142 million for each of fiscal 2019 and 2018 and $147 million for fiscal 2017.

Purification Solutions Goodwill and Long-Lived Assets Impairment Charges

12 Months Ended

Sep. 30, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

Purification Solutions Goodwill and Long-Lived Assets Impairment Charges

Note G. Purification Solutions Goodwill and Long-Lived Assets Impairment Charges

During the second quarter of fiscal 2018, the Company recorded impairment charges relating to the goodwill and long-lived assets of the Purification Solutions reporting unit, and an associated deferred tax benefit, in the Consolidated Statements of Operations as follows:

	Three Months Ended March 31, 2018
	(In millions)
Purification Solutions goodwill impairment charge	$	92
Purification Solutions long-lived assets impairment charge		162
Benefit for income taxes		(30	)
Impairment charges, after tax	$	224

In the second quarter of fiscal 2018, the Purification Solutions reporting unit had experienced market share losses, lower customer demand and declining prices in the mercury removal and North America powdered activated carbon applications, which led the Company to reassess its previous estimates for expected growth in volumes, prices and margins in the reporting unit. Due to the revised forecasts at the time, the Company performed a quantitative goodwill impairment test and determined that the estimated fair value of the Purification Solutions reporting unit was lower than the reporting unit's carrying value, resulting in a goodwill impairment charge of $92 million.

Prior to determining the goodwill impairment charge, the Company considered whether the assets of the reporting unit, which is also considered the asset group, were recoverable. As a result of this assessment, the Company recorded an inventory reserve adjustment of $13 million and impairments to long lived assets of $162 million. The adjustment to inventory carrying value was determined based on reassessments of volumes, pricing, and margins for the reporting unit at the time and was recorded in Cost of sales in the Consolidated Statements of Operations. The impairment analysis to assess if definite-lived intangible assets and property, plant and equipment were recoverable was based on the estimated undiscounted cash flows of the reporting unit, and these cash flows were not sufficient to recover the carrying value of the long-lived assets over their remaining useful lives. Accordingly, the Company recorded impairment charges of $64 million and $98 million, to its definite-lived intangible assets and property, plant and equipment, respectively, in the second quarter of fiscal 2018 based on the lower of the carrying amount or fair value of the long-lived assets.

Cabot will continue to monitor for events or changes in business circumstances that may indicate that the remaining carrying value of the asset group may not be recoverable.

The Company recorded a tax benefit related to the impairment charges of $30 million in the second quarter of fiscal 2018 which was subsequently reduced by $1 million after the impairment charges by tax jurisdiction were finalized in the fourth quarter of fiscal 2018.

Goodwill and Intangible Assets

12 Months Ended

Sep. 30, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

Goodwill and Intangible Assets

Note H. Goodwill and Intangible Assets

The carrying amount of goodwill attributable to each reportable segment with goodwill balances and the changes in those balances during the period ended September 30, 2019 are as follows:

	Reinforcement Materials			Performance Chemicals			Purification Solutions ⁽¹⁾		Total
	(In millions)
Balance at September 30, 2018	$	52		$	41		$	—	$	93
Foreign currency impact		(2	)		(1	)		—		(3	)
Balance at September 30, 2019	$	50		$	40		$	—	$	90

⁽¹⁾

^{The Company has incurred $444 million accumulated impairment losses associated with the goodwill of the Purification Solutions segment as of both September 30, 2019 and September 30, 2018. There are no accumulated impairment losses associated with the goodwill of the Reinforcement Materials or Performance Chemicals segments.}

The following table provides information regarding the Company’s intangible assets:

	September 30, 2019							September 30, 2018
	Gross Carrying Value		Accumulated Amortization			Net Intangible Assets		Gross Carrying Value		Accumulated Amortization			Net Intangible Assets
	(In millions)
Intangible assets with finite lives
Developed technologies	$	50	$	(5	)	$	45	$	52	$	(2	)	$	50
Trademarks		8		—			8		8		—			8
Customer relationships		57		(14	)		43		51		(11	)		40
Total intangible assets	$	115	$	(19	)	$	96	$	111	$	(13	)	$	98

Intangible assets are amortized over their estimated useful lives, which range between twelve and twenty-five years, with a weighted average amortization period of approximately 19 years. Amortization expense for the years ended September 30, 2019, 2018 and 2017 was $6 million, $7 million and $8 million, respectively, and is included in Cost of sales, Selling and administrative expenses, and Research and technical expenses in the Consolidated Statements of Operations. Total amortization expense is estimated to be approximately $6 million each year for the next five fiscal years.

Accounts Payable, Accrued Liabilities and Other Liabilities

12 Months Ended

Sep. 30, 2019

Payables And Accruals [Abstract]

Accounts Payable, Accrued Liabilities and Other Liabilities

Note I. Accounts Payable, Accrued Liabilities and Other Liabilities

Accounts payable and accrued liabilities included in current liabilities consist of the following:

	September 30
	2019		2018
	(In millions)
Accounts payable	$	390	$	446
Accrued employee compensation		51		70
Other accrued liabilities		96		97
Total	$	537	$	613

Other long-term liabilities consist of the following:

	September 30
	2019		2018
	(In millions)
Employee benefit plan liabilities	$	91	$	118
Non-current tax liabilities		12		19
Other accrued liabilities		103		115
Total	$	206	$	252

Debt and Other Obligations

12 Months Ended

Sep. 30, 2019

Debt Disclosure [Abstract]

Debt and Other Obligations

Note J. Debt and Other Obligations

Long-term Obligations

The Company’s long-term obligations, the fiscal year in which they mature and their respective interest rates are summarized below:

	September 30
	2019			2018
	(In millions)
Variable Rate Debt:
Revolving Credit Facility, expires fiscal 2023	$	—		$	—
Revolving Credit Facility - Canada, expires fiscal 2021		43			90
Revolving Credit Facility - Euro, expires fiscal 2024		56			—
Total variable rate debt		99			90
Fixed Rate Debt:
3.7% Notes due fiscal 2022		350			350
3.4% Notes due fiscal 2026		250			250
4.0% Notes due fiscal 2029		300			—
Medium Term Notes:
Notes matured fiscal 2019, 7.42%		—			30
Notes due fiscal 2022, 8.34% — 8.47%		15			15
Notes due fiscal 2028, 6.57% — 7.28%		8			8
Total Medium Term Notes		23			53
Chinese Renminbi Debt, matured fiscal 2019, 4.35%		—			4
Chinese Renminbi Debt, due fiscal 2020, 4.35%		4			—
Total fixed rate debt		927			657
Capital lease obligations, due through fiscal 2033		12			11
Unamortized debt issuance costs and debt discount		(7	)		(4	)
Total debt		1,031			754
Less current portion of long-term debt		(7	)		(35	)
Total long-term debt	$	1,024		$	719

Revolving Credit Facility, expiring fiscal 2023— In October 2015, the Company entered into a revolving credit agreement with a loan commitment not to exceed $1 billion. The amount available for borrowing under the revolving credit agreement was $967 million as of September 30, 2019. The revolving credit agreement, which matures on October 23, 2022, supports the Company’s commercial paper program. Borrowings may be used for working capital, letters of credit and other general corporate purposes. The revolving credit agreement contains affirmative and negative covenants, a single financial covenant (consolidated total debt to consolidated EBITDA, as defined in the credit agreement) and events of default customary for financings of this type.

Revolving Credit Facility-Canada expiring fiscal 2021—In September 2018, a Canadian subsidiary entered into a revolving credit agreement with a loan commitment not to exceed 100 million U.S. dollars. The amount available for borrowing under this revolving credit agreement was $57 million as of September 30, 2019, and the weighted average interest rate on the outstanding balance during the year was 3.21%. The revolving credit agreement, which matures on September 24, 2021, subject to the right to request a one-year extension, may be used for working capital, capital expenditures and other general corporate purposes. The revolving credit agreement is guaranteed by Cabot Corporation.

Revolving Credit Facility-Euro, expiring fiscal 2024—In May 2019, several subsidiaries entered into a revolving credit agreement with a loan commitment not to exceed 300 million Euros. The amount available for borrowing under this revolving credit agreement was $272 million as of September 30, 2019, and the weighted average interest rate on the outstanding balance during the year was 3.42%. The revolving credit agreement, which matures on the earlier of (i) May 22, 2024 and (ii) the date of maturity, termination or expiration of the Corporate revolving credit facility, may be used for repatriation of earnings of Cabot’s foreign subsidiaries to the U.S., the repayment of indebtedness of the Company’s foreign subsidiaries owing to the Company or any of its subsidiaries, and for working capital and general corporate purposes. The obligations of the subsidiaries under the revolving credit agreement are guaranteed by the Company. The Company paid debt issuance costs of $1 million upon entering the agreement, which are being amortized over the life of the revolver.

Chinese Renminbi Debt—The Company’s consolidated Chinese subsidiaries had $4 million of unsecured long-term debt outstanding with a noncontrolling shareholder of a consolidated subsidiary as of both September 30, 2019 and 2018.

2.55% Notes matured fiscal 2018—In July 2012, Cabot issued $250 million in registered notes with a coupon of 2.55% that matured on January 15, 2018. These notes were unsecured and paid interest on January 15 and July 15. The net proceeds of this offering were $248 million after deducting discounts and issuance costs. The discount of less than $1 million was recorded at issuance and was amortized over the life of the notes. The notes were paid in full during the second quarter of fiscal 2018.

3.7% Notes due fiscal 2022—In July 2012, Cabot issued $350 million in registered notes with a coupon of 3.7% that mature on July 15, 2022. These notes are unsecured and pay interest on January 15 and July 15. The net proceeds of this offering were $347 million after deducting discounts and issuance costs. The discount of less than $1 million was recorded at issuance and is being amortized over the life of the notes.

3.4% Notes due fiscal 2026—In September 2016, Cabot issued $250 million in registered notes with a coupon of 3.4% that mature on September 15, 2026. These notes are unsecured and pay interest on March 15 and September 15. The net proceeds of this offering were $248 million after deducting discounts and issuance costs. The discount of less than $1 million was recorded at issuance and is being amortized over the life of the notes.

4.0% Notes due fiscal 2029—In June 2019, Cabot issued $300 million in registered, unsecured, notes with a coupon of 4.0% that mature on July 1, 2029. Interest is payable under the notes semi-annually on January 1 and July 1 commencing in January 2020. The net proceeds of this offering were $296 million after deducting discounts and issuance costs of $1 million and $3 million, respectively, which were paid at issuance and are being amortized over the life of the notes.

Medium Term Notes—At September 30, 2019 and 2018, there were $23 million and $53 million, respectively, of unsecured medium term notes outstanding issued to numerous lenders with various fixed interest rates and maturity dates. The weighted average maturity of the total outstanding medium term notes is 5 years with a weighted average interest rate of 7.96%.

Capital Lease Obligations—Cabot had capital lease obligations for certain equipment and buildings with a recorded value of $12 million and $11 million at September 30, 2019 and 2018, respectively. Cabot will make payments totaling $21 million over the next 14 years, including $9 million of imputed interest. At both September 30, 2019 and 2018, the original cost of capital lease assets was $20 million. At both September 30, 2019 and 2018, the associated accumulated depreciation of assets under capital leases was $13 million. The amortization related to those assets under capital lease is included in depreciation expense.

Future Years Payment Schedule

The aggregate principal amounts of long-term debt and capital lease obligations due in each of the five years from fiscal 2020 through 2024 and thereafter are as follows:

Years Ending September 30	Principal Payments on Long-Term Debt		Payments on Capital Lease Obligations			Total
	(In millions)
2020	$	4	$	3		$	7
2021		43		3			46
2022		365		3			368
2023		—		3			3
2024		56		2			58
Thereafter		558		7			565
Less: Interest		—		(9	)		(9	)
Total	$	1,026	$	12		$	1,038

Standby letters of credit—At September 30, 2019, the Company had provided standby letters of credit that were outstanding and not drawn totaling $5 million, which expire through fiscal 2020.

Short-term Borrowings

Commercial Paper—The Company has a commercial paper program and the maximum aggregate balance of commercial paper notes outstanding and the amounts borrowed under the revolving credit facility may not exceed the borrowing capacity of $1 billion under the revolving credit facility. The proceeds from the issuance of the commercial paper have been used for general corporate purposes, which may include working capital, refinancing existing indebtedness, capital expenditures, share repurchases, and acquisitions. The revolving credit facility is available to repay the outstanding commercial paper, if necessary.

There was an outstanding balance of commercial paper of $33 million as of September 30, 2019 with a weighted average interest rate of 2.27% and an outstanding balance of $249 million as of September 30, 2018 with a weighted average interest rate of 2.36%.

Short-term Notes Payable—There were no short term notes payable as of both September 30, 2019 and 2018.

Redeemable Preferred Stock

In November 2013, the Company purchased all of its joint venture partner’s common stock in the former NHUMO, S.A. de C.V. (“NHUMO”) joint venture. At the close of the transaction, NHUMO issued redeemable preferred stock to the joint venture partner with a repurchase value of $25 million and a fixed dividend rate of 6% per annum. In November 2018, the Company repurchased the preferred stock for $25 million and paid a final dividend payment of approximately $1.4 million. The preferred stock was accounted for as a financing obligation and was separately presented in the Consolidated Balance Sheets as a current liability as of September 30, 2018.

Financial Instruments and Fair Value Measurements

12 Months Ended

Sep. 30, 2019

Fair Value Disclosures [Abstract]

Financial Instruments and Fair Value Measurements

Note K. Financial Instruments and Fair Value Measurements

The FASB authoritative guidance on fair value measurements defines fair value, provides a framework for measuring fair value, and requires certain disclosures about fair value measurements. The required disclosures focus on the inputs used to measure fair value. The guidance establishes the following hierarchy for categorizing these inputs:

Level 1	—	Quoted market prices in active markets for identical assets or liabilities

Level 2	—	Significant other observable inputs (e.g., quoted prices for similar items in active markets, quoted prices for identical or similar items in markets that are not active, inputs other than quoted prices that are observable such as interest rate and yield curves, and market-corroborated inputs)

Level 3	—	Significant unobservable inputs

There were no transfers of financial assets or liabilities measured at fair value between Level 1 and Level 2, and there were no Level 3 investments during fiscal 2019 or 2018.

At both September 30, 2019 and 2018, Cabot had derivatives relating to foreign currency risks carried at fair value. At September 30, 2019, the fair value of these derivatives was a net asset of $1 million and was included in Prepaid expenses and other current assets and Other assets on the Consolidated Balance Sheets. At September 30, 2018, the fair value of these derivatives was a net liability of $18 million and was included in Prepaid expenses and other current assets and Other liabilities on the Consolidated Balance Sheets. These derivatives are classified as Level 2 instruments within the fair value hierarchy as the fair value determination was based on observable inputs.

At September 30, 2019 and 2018, the fair value of Guaranteed investment contracts, included in Other assets on the Consolidated Balance Sheets, was $10 million and $11 million, respectively. Guaranteed investment contracts were classified as Level 2 instruments within the fair value hierarchy as the fair value determination was based on other observable inputs.

At both September 30, 2019 and 2018, the fair values of cash and cash equivalents, accounts and notes receivable, accounts payable and accrued liabilities, and short term borrowings and variable rate debt approximated their carrying values due to the short-term nature of these instruments. The carrying value and fair value of the long-term fixed rate debt were $1,026 million and $1,095 million, respectively, as of September 30, 2019 and $747 million and $742 million, respectively, as of September 30, 2018. The fair values of Cabot’s fixed rate long-term debt are estimated based on comparable quoted market prices at the respective period ends. The carrying amounts of Cabot’s floating rate long-term debt and capital lease obligations approximate their fair values. All such measurements are based on observable inputs and are classified as Level 2 within the fair value hierarchy. The valuation technique used is the discounted cash flow model.

Derivatives

12 Months Ended

Sep. 30, 2019

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Derivatives

Note L. Derivatives

Risk Management

Cabot’s business operations are exposed to changes in interest rates, foreign currency exchange rates and commodity prices because Cabot finances certain operations through long and short-term borrowings, denominates transactions in a variety of foreign currencies and purchases certain commoditized raw materials. Changes in these rates and prices may have an impact on future cash flows and earnings. The Company manages these risks through normal operating and financing activities and, when deemed appropriate, through the use of derivative financial instruments.

The Company has policies governing the use of derivative instruments and does not enter into financial instruments for trading or speculative purposes.

By using derivative instruments, Cabot is subject to credit and market risk. If a counterparty fails to fulfill its performance obligations under a derivative contract, Cabot’s credit risk will equal the fair value of the derivative. Generally, when the fair value of a derivative contract is positive, the counterparty owes Cabot, thus creating a payment risk for Cabot. The Company minimizes counterparty credit (or repayment) risk by entering into transactions with major financial institutions of investment grade credit rating. Cabot’s exposure to market risk is not hedged in a manner that completely eliminates the effects of changing market conditions on earnings or cash flow. No significant concentration of credit risk existed at September 30, 2019 and 2018.

Interest Rate Risk Management

Cabot’s objective is to maintain a certain fixed-to-variable interest rate mix on the Company’s debt obligations. Cabot may enter into interest rate swaps as a hedge of the underlying debt instruments to effectively change the characteristics of the interest rate without changing the debt instrument. As of both September 30, 2019 and 2018, there were no derivatives held to manage interest rate risk.

Foreign Currency Risk Management

Cabot’s international operations are subject to certain risks, including currency exchange rate fluctuations and government actions. Cabot endeavors to match the currency in which debt is issued to the currency of the Company’s major, stable cash receipts. In some situations, Cabot has issued debt denominated in U.S. dollars and then entered into cross-currency swaps that exchange the dollar principal and interest payments into Euro denominated principal and interest payments.

Additionally, the Company has foreign currency exposure arising from its net investments in foreign operations. Cabot may enter into cross-currency swaps to mitigate the impact of currency rate changes on the Company’s net investments.

The Company also has foreign currency exposure arising from the denomination of monetary assets and liabilities in foreign currencies other than the functional currency of a given subsidiary as well as the risk that currency fluctuations could affect the dollar value of future cash flows generated in foreign currencies. Accordingly, Cabot uses short-term forward contracts to minimize the exposure to foreign currency risk. In certain situations where the Company has forecasted purchases under a long-term commitment or forecasted sales denominated in a foreign currency, Cabot may enter into appropriate financial instruments in accordance with the Company’s risk management policy to hedge future cash flow exposures.

The following table provides details of the derivatives held as of September 30, 2019 and 2018 to manage foreign currency risk.

		Notional Amount
Description	Borrowing	September 30, 2019	September 30, 2018	Hedge Designation
Cross Currency Swaps	3.4% Notes	USD 250 million swapped to EUR 223 million	USD 250 million swapped to EUR 223 million	Net investment
Forward Foreign Currency Contracts⁽¹⁾	N/A	USD 54 million	USD 18 million	No designation

⁽¹⁾	Cabot’s forward foreign exchange contracts are denominated in British pound, Canadian dollar, Indonesian rupiah and Czech koruna.

Accounting for Derivative Instruments and Hedging Activities

The Company determines the fair value of financial instruments using quoted market prices whenever available. When quoted market prices are not available for various types of financial instruments (such as forwards, options and swaps), the Company uses standard models with market-based inputs, which take into account the present value of estimated future cash flows and the ability of Cabot or the financial counterparty to perform. For interest rate and cross-currency swaps, the significant inputs to these models are interest rate curves for discounting future cash flows and are adjusted for credit risk. For forward foreign currency contracts, the significant inputs are interest rate curves for discounting future cash flows, and exchange rate curves of the foreign currency for translating future cash flows.

Fair Value Hedge

For derivative instruments that are designated and qualify as fair value hedges, the gain or loss on the derivative as well as the offsetting gain or loss on the hedged item attributable to the hedged risk are recognized in current period earnings.

Cash Flow Hedge

For derivative instruments that are designated and qualify as cash flow hedges, the effective portion of the gain or loss on the derivative is recorded in AOCI and reclassified to earnings in the same period or periods during which the hedged transaction affects earnings. Gains and losses on the derivative representing either hedge ineffectiveness or hedge components excluded from the assessment of effectiveness are recognized in current period earnings.

Net Investment Hedge

For net investment hedges, changes in the fair value of the effective portion of the derivatives’ gains or losses are reported as foreign currency translation gains or losses in AOCI while changes in the ineffective portion are reported in earnings. Effectiveness is assessed based on the hypothetical derivative method. The gains or losses on derivative instruments reported in AOCI are reclassified to earnings in the period in which earnings are affected by the underlying item, such as a disposal or substantial liquidations of the entities being hedged.

The Company has cross-currency swaps with a notional amount of $250 million, which are designated as hedges of its net investments in certain Euro denominated subsidiaries. Cash settlements occur semi-annually on March 15^th and September 15^th for fixed rate interest payments and a cash exchange of the notional currency amount will occur at the end of the term in 2026. During fiscal 2019 and fiscal 2018, the Company received net cash interest of $4 million and $3 million, respectively. As of September 30, 2019, the fair value of these swaps was a net asset of $1 million and was included in Prepaid expenses and other current assets and Other assets, and the cumulative gain of $5 million was included in AOCI on the Consolidated Balance Sheets. As of September 30, 2018, the fair value of these swaps was a net liability of $18 million and was included in Prepaid expenses and other current assets and Other liabilities, and the cumulative loss of $14 million was included in AOCI on the Consolidated Balance Sheets.

The following table summarizes the impact of the cross-currency swaps to AOCI and the Consolidated Statements of Operations:

	Years Ended September 30
	2019		2018			2017			2019			2018			2017		2019		2018		2017
Description	Gain/(Loss) Recognized in AOCI								(Gain)/Loss Reclassified from AOCI into Interest Expense in the Consolidated Statements of Operations								(Gain)/Loss Recognized in Interest Expense in the Consolidated Statements of Operations (Amount Excluded from Effectiveness Testing)
	(In millions)
Cross-currency swaps	$	23	$	(2	)	$	(10	)	$	(5	)	$	(5	)	$	—	$	1	$	2	$	—

Other Derivative Instruments

From time to time, the Company may enter into certain derivative instruments that may not be designated as hedges for accounting purposes, which may include cross-currency swaps, foreign currency forward contracts and commodity derivatives. For cross-currency swaps and foreign currency forward contracts not designated as hedges, the Company uses standard models with market-based inputs. The significant inputs to these models are interest rate curves for discounting future cash flows, and exchange rate curves of the foreign currency for translating future cash flows. In determining the fair value of the commodity derivatives, the significant inputs to valuation models are quoted market prices of similar instruments in active markets. Although these derivatives do not qualify for hedge accounting, Cabot believes that such instruments are closely correlated with the underlying exposure, thus managing the associated risk. The gains or losses from changes in the fair value of derivative instruments that are not accounted for as hedges are recognized in current period earnings.

At both September 30, 2019 and 2018, the fair value of derivative instruments not designated as hedges were immaterial. At September 30, 2019 and 2018, these instruments were presented in Prepaid expenses and other current assets and Accounts payable and accrued liabilities and, respectively, on the Consolidated Balance Sheets.

Hyperinflationary Economies

12 Months Ended

Sep. 30, 2019

Equity Method Investments And Joint Ventures [Abstract]

Hyperinflationary Economies

Note M. Hyperinflationary Economies

Argentina

Cabot owns 100% of a carbon black operating entity in Argentina. Beginning on July 1, 2018, the operating entity was considered to be functioning in a highly inflationary economy and began using Cabot’s reporting currency, the U.S. dollar, as its functional currency. There was no financial statement impact at the date of conversion due to the change in functional currency. Since the conversion, all impacts of foreign exchange changes between the reporting currency and Argentine peso are reflected in earnings in the Consolidated Statements of Operations.

The Company’s income from operations was not significantly impacted from this change since the operating entity’s sales and a portion of its raw material purchases were already denominated in U.S. dollars. The operating entity’s net revenue represented approximately 3% and 2% of Cabot’s total net revenue for the years ended September 30, 2019 and 2018, respectively.

The operating entity’s assets and liabilities held in local currency, which consist primarily of cash and cash equivalents, inventories, property, plant and equipment and accounts payable and accrued liabilities, made up less than 2% of Cabot’s total assets and total liabilities as of both September 30, 2019 and 2018. Changes in the Argentine peso exchange rate result in foreign currency exchange gains or losses on the operating entity’s peso-denominated monetary assets and liabilities. For the years ended September 30, 2019 and 2018, the Company recorded a net gain of $2 million and $3 million, respectively, within Other

(income) expense in the Consolidated Statements of Operations, which reflects the remeasurement of the operating entity’s net monetary liabilities denominated in Argentine pesos using an exchange rate of 57.32 and 39.70 Argentine pesos to the U.S. dollar at September 30, 2019 and 2018, respectively.

The Company will continue to monitor the developments in Argentina and their potential impact on the operating entity’s operations or carrying value.

Venezuela

Cabot owns 49% of a carbon black operating entity in Venezuela, which is accounted for as an equity affiliate, through wholly-owned subsidiaries that carry the investment and receive its dividends. While the operating entity has historically been profitable, it has not been operational in recent periods due to a lack of available raw materials, which is expected to continue for the foreseeable future. As such, in the second quarter of fiscal 2019, the Company performed an impairment analysis and determined that the decrease in fair value of the Venezuelan equity investment is other-than-temporary and that the investment is fully impaired. The Company recorded an impairment charge of $11 million in the second quarter of fiscal 2019, which is included in Other income (expense) within the Consolidated Statement of Operations.

Employee Benefit Plans

12 Months Ended

Sep. 30, 2019

Compensation And Retirement Disclosure [Abstract]

Employee Benefit Plans

Note N. Employee Benefit Plans

The information below provides detail concerning the Company’s benefit obligations under the defined benefit and postretirement benefit plans it sponsors.

Defined benefit plans provide pre-determined benefits to employees that are distributed upon retirement. Cabot is making all sponsor required contributions to these plans. The accumulated benefit obligation was $157 million for the U.S. defined benefit plans and $205 million for the foreign plans as of September 30, 2019 and $143 million for the U.S. defined benefit plans and $349 million for the foreign plans as of September 30, 2018.

In addition to benefits provided under the defined benefit and postretirement benefit plans, the Company provides benefits under defined contribution plans. Cabot recognized expenses related to these plans of $20 million in fiscal 2019, $19 million in fiscal 2018 and $18 million in fiscal 2017.

The following provides information about projected benefit obligations, plan assets, the funded status and weighted-average assumptions of the defined benefit pension and postretirement benefit plans:

	Years Ended September 30
	2019						2018						2019						2018
	Pension Benefits												Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign			U.S.			Foreign
	(In millions)
Change in Benefit Obligations:
Benefit obligation at beginning of year	$	143		$	373		$	160		$	376		$	29		$	19		$	33		$	20
Service cost		1			7			1			9			—			—			—			—
Interest cost		5			5			5			7			1			1			1			1
Plan participants’ contribution		—			1			—			2			—			—			—			—
Foreign currency exchange rate changes		—			(13	)		—			(7	)		—			(1	)		—			(1	)
(Gain) Loss from changes in actuarial assumptions and plan experience		21			—			(10	)		2			1			2			(2	)		—
Benefits paid		(11	)		(7	)		(7	)		(13	)		(3	)		(1	)		(3	)		(1	)
Settlements or curtailments		(1	)		(134	)		(5	)		(2	)		—			—			—			—
Divestiture of Specialty Fluids		—			(13	)		—			—			—			—			—			—
Other		(1	)		1			(1	)		(1	)		—			—			—			—
Benefit obligation at end of year	$	157		$	220		$	143		$	373		$	28		$	20		$	29		$	19

	Years Ended September 30
	2019						2018						2019						2018
	Pension Benefits												Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign			U.S.			Foreign
	(In millions)
Change in Plan Assets:
Fair value of plan assets at beginning of year	$	149		$	323		$	156		$	318		$	—		$	—		$	—		$	—
Actual return on plan assets		14			17			4			17			—			—			—			—
Employer contribution		1			7			1			9			3			1			3			1
Plan participants’ contribution		—			1			—			2			—			—			—			—
Foreign currency exchange rate changes		—			(11	)		—			(7	)		—			—			—			—
Benefits paid		(11	)		(7	)		(7	)		(13	)		(3	)		(1	)		(3	)		(1	)
Settlements		(1	)		(124	)		(4	)		(2	)		—			—			—			—
Divestiture		—			(10	)		—			—			—			—			—			—
Expenses paid from assets		(1	)		(1	)		(1	)		(1	)		—			—			—			—
Fair value of plan assets at end of year	$	151		$	195		$	149		$	323		$	—		$	—		$	—		$	—
Funded status	$	(6	)	$	(25	)	$	6		$	(50	)	$	(28	)	$	(20	)	$	(29	)	$	(19	)
Recognized asset (liability)	$	(6	)	$	(25	)	$	6		$	(50	)	$	(28	)	$	(20	)	$	(29	)	$	(19	)

Pension Assumptions and Strategy

The following assumptions were used to determine the pension benefit obligations and periodic benefit costs as of and for the years ended September 30:

	2019						2018						2017
	Pension Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign
Actuarial assumptions as of the year-end measurement date:
Discount rate		2.6	%		1.8	%		4.2	%		2.4	%		3.6	%		2.4	%
Rate of increase in compensation	N/A				3.0	%	N/A				2.7	%	N/A				2.7	%
Actuarial assumptions used to determine net periodic benefit cost during the year:
Discount rate - benefit obligation		4.2	%		2.4	%		3.6	%		2.4	%		3.4	%		1.8	%
Discount rate - service cost	N/A				2.5	%	N/A				2.4	%	N/A				1.8	%
Discount rate - interest cost		3.9	%		2.1	%		3.0	%		2.0	%		2.7	%		1.5	%
Expected long-term rate of return on plan assets		6.3	%		4.9	%		6.8	%		4.9	%		6.8	%		4.7	%
Rate of increase in compensation	N/A				2.7	%	N/A				2.7	%	N/A				2.8	%

Postretirement Assumptions and Strategy

The following assumptions were used to determine the postretirement benefit obligations and net costs as of and for the years ended September 30:

	2019						2018						2017
	Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign
Actuarial assumptions as of the year-end measurement date:
Discount rate		2.9	%		2.4	%		4.1	%		3.2	%		3.4	%		3.1	%
Initial health care cost trend rate		6.5	%		6.9	%		7.0	%		7.0	%		7.0	%		7.1	%
Actuarial assumptions used to determine net cost during the year:
Discount rate - benefit obligation		4.1	%		3.2	%		3.4	%		3.1	%		3.0	%		2.8	%
Discount rate - service cost		4.0	%		3.5	%		3.1	%		3.6	%		2.6	%		3.2	%
Discount rate - interest cost		3.7	%		3.1	%		2.8	%		3.0	%		2.4	%		2.6	%
Initial health care cost trend rate		7.0	%		7.0	%		7.0	%		7.1	%		7.0	%		6.1	%

Cabot uses discount rates as of September 30, the plans’ measurement date, to determine future benefit obligations under its U.S. and foreign defined benefit plans. The discount rates for the defined benefit plans in Canada, the Eurozone, Japan, Mexico, Switzerland, the United Arab Emirates, the United Kingdom and the U.S. are derived from yield curves that reflect high quality corporate bond yield or swap rate information in each region and reflect the characteristics of Cabot’s employee benefit plans. The discount rates for the defined benefit plans in the Czech Republic and Indonesia are based on government bond indices that best reflect the durations of the plans, adjusted for credit spreads presented in selected AA corporate bond indices. The rates utilized are selected because they represent long-term, high quality, fixed income benchmarks that approximate the long-term nature of Cabot’s pension obligations and related payouts.

Amounts recognized in the Consolidated Balance Sheets at September 30, 2019 and 2018 related to the Company's defined benefit pension and postretirement benefit plans were as follows:

	September 30
	2019						2018						2019						2018
	Pension Benefits												Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign			U.S.			Foreign
	(In millions)
Noncurrent assets	$	—		$	19		$	10		$	21		$	—		$	—		$	—		$	—
Current liabilities	$	(3	)	$	(1	)	$	—		$	(1	)	$	(3	)	$	—		$	(3	)	$	(1	)
Noncurrent liabilities	$	(3	)	$	(43	)	$	(4	)	$	(70	)	$	(25	)	$	(20	)	$	(26	)	$	(18	)

Amounts recognized in AOCI at September 30, 2019 and 2018 related to the Company's defined benefit pension and postretirement benefit plans were as follows:

	September 30
	2019				2018						2019					2018
	Pension Benefits										Postretirement Benefits
	U.S.		Foreign		U.S.			Foreign			U.S.			Foreign		U.S.			Foreign
	(In millions)
Net actuarial (gain) loss	$	13	$	36	$	(1	)	$	49		$	(6	)	$	6	$	(7	)	$	4
Net prior service credit		—		—		—			(1	)		—			—		(2	)		—
Balance in accumulated other comprehensive income (loss), pretax	$	13	$	36	$	(1	)	$	48		$	(6	)	$	6	$	(9	)	$	4

In fiscal 2020, the Company expects an estimated net loss of $3 million will be amortized from AOCI to net periodic benefit cost. In addition, the Company expects no prior service credits for other postretirement benefits will be amortized from AOCI to net periodic benefit costs in fiscal 2020.

Estimated Future Benefit Payments

The Company expects that the following benefit payments will be made to plan participants in the years from 2020 to 2029:

	Pension Benefits				Postretirement Benefits
Years Ending September 30	U.S.		Foreign		U.S.		Foreign
	(In millions)
2020⁽¹⁾	$	158	$	9	$	3	$	1
2021	$	—	$	12	$	3	$	1
2022	$	—	$	10	$	3	$	1
2023	$	—	$	10	$	3	$	1
2024	$	—	$	11	$	3	$	1
2025 - 2029	$	1	$	55	$	10	$	4

⁽¹⁾	^{The $158 million expected payment for U.S. pension benefits in fiscal 2020 is in connection with the termination of the U.S. plan which is expected to be completed in fiscal 2020.}

Postretirement medical benefits are unfunded and impact Cabot’s cash flows as benefits become due, which is expected to be $4 million in fiscal 2020. The Company expects to contribute $10 million to its pension plans in fiscal 2020.

Net periodic defined benefit pension and other postretirement benefit costs include the following components:

	Years Ended September 30
	2019						2018						2017						2019					2018					2017
	Pension Benefits																		Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign			U.S.			Foreign		U.S.			Foreign		U.S.			Foreign
	(In millions)
Service cost	$	1		$	7		$	1		$	9		$	1		$	10		$	—		$	—	$	—		$	—	$	—		$	—
Interest cost		5			5			5			7			4			6			1			1		1			1		1			1
Expected return on plan assets		(9	)		(10	)		(10	)		(15	)		(9	)		(14	)		—			—		—			—		—			—
Amortization of prior service cost		—			2			—			—			—			—			(2	)		—		(3	)		—		(3	)		—
Net losses		—			2			—			3			—			5			(1	)		—		(1	)		—		—			—
Settlements or Curtailments cost		—			(7	)		—			—			—			—			—			—		—			—		—			—
Net periodic (benefit) cost	$	(3	)	$	(1	)	$	(4	)	$	4		$	(4	)	$	7		$	(2	)	$	1	$	(3	)	$	1	$	(2	)	$	1

Other changes in plan assets and benefit obligations recognized in Other comprehensive income (loss) are as follows:

	Years Ended September 30
	2019					2018						2017						2019				2018						2017
	Pension Benefits																	Postretirement Benefits
	U.S.		Foreign			U.S.			Foreign			U.S.			Foreign			U.S.		Foreign		U.S.			Foreign			U.S.			Foreign
	(In millions)
Net (gains) losses	$	14	$	(16	)	$	(4	)	$	—		$	(9	)	$	(35	)	$	—	$	2	$	(2	)	$	(1	)	$	(3	)	$	(1	)
Prior service (credit) cost		—		3			—			—			—			—			—		—		—			—			—			—
Amortization of prior service credit		—		(2	)		—			—			—			—			2		—		3			—			3			—
Amortization of prior unrecognized loss		—		(2	)		—			(3	)		—			(5	)		1		—		1			—			—			—
Loss on divestiture		—		(2	)		—			—			—			—			—		—		—			—			—			—
Gain on settlements		—		7			—			—			—			—			—		—		—			—			—			—
Other		—		—			—			—			—			—			—		—		—			—			—			—
Net changes recognized in Total other comprehensive (income) loss ⁽¹⁾	$	14	$	(12	)	$	(4	)	$	(3	)	$	(9	)	$	(40	)	$	3	$	2	$	2		$	(1	)	$	—		$	(1	)

⁽¹⁾	^{The tax impact on pension and other postretirement benefit liability adjustments arising during the period was a tax benefit of $5 million, tax provision of $1 million, and tax provision of $7 million for fiscal years 2019, 2018, and 2017, respectively.}

In the third quarter of fiscal 2019, the Company adjusted the assumptions in its U.K. plan to calculate accrued benefits for a portion of the plan’s participants. As a result of this change, a prior service cost of $2 million was recorded in Other income (expense) in the Consolidated Statement of Operations.

Curtailments and Settlements of Employee Benefit Plans

In fiscal 2019, the Company transferred the defined benefit obligations and pension plan assets in one of its foreign defined benefit plans to a multi-employer plan. This action moved the administrative, asset custodial, asset investment, actuarial, communication and benefit payment obligations to the multi-employer fund administrator. As a result of the transfer, there was a $30 million reduction in net pension obligations associated with the plan, and a pre-tax gain of $7 million was recorded in Other income (expense) in the Consolidated Statement of Operations. In addition, as part of the transfer the Company recorded a $3 million charge in fiscal 2019 for the Company’s agreement to fund the actuarial loss gap between the terminated plan and the multi-employer plan, which will be paid over the next five years. This charge is included Other income (expense) in the Consolidated Statement of Operations and the liability is included in Accounts payable and accrued liabilities and Other liabilities on the Consolidated Balance Sheet.

The Company recognized net losses of less than $1 million in fiscal 2018 and 2017 due to curtailments and settlements of certain employee benefit plans.

U.S. Plan Termination

In fiscal 2019, the Company’s Board of Directors approved a resolution to terminate the U.S. pension plan. The Company commenced the U.S. plan termination process during the third quarter of 2019 and expects to complete the transfer of the U.S. plan’s assets in fiscal year 2020 pending an Internal Revenue Service (“IRS”) determination letter. The pension liability will be settled in either a lump-sum payment or a purchased annuity. Upon settlement of the plan, the Company will recognize a loss associated with the release of approximately $13 million from Accumulated other comprehensive income (loss) in the Consolidated Balance Sheet to Other income (expense) in the Consolidated Statement of Operations.

Sensitivity Analysis

Measurement of postretirement benefit expense is based on actuarial assumptions used to value the postretirement benefit liability at the beginning of the year. Assumed health care cost trend rates have an effect on the amounts reported for the health care plans. The fiscal 2019 weighted-average assumed health care cost trend rate is 6.5% for U.S. plans and 6.9 % for foreign plans. A one percentage point change in the 2019 assumed health care cost trend rate would have an immaterial impact to the aggregate of the service and interest cost components of the net periodic postretirement benefit and would have a less than $1 million impact to U.S. plans and $3 million impact to foreign plans postretirement benefit obligation.

Plan Assets

The Company’s defined benefit pension plans weighted-average asset allocations at September 30, 2019 and 2018 by asset category, are as follows:

	September 30
	2019						2018
	Pension Assets
	U.S.			Foreign			U.S.			Foreign
Equity securities		—	%		39	%		40	%		39	%
Debt securities		68	%		50	%		60	%		53	%
Cash and other securities		32	%		11	%		—	%		8	%
Total		100	%		100	%		100	%		100	%

To develop the expected long-term rate of return on plan assets assumption, the Company used a capital asset pricing model. The model considers the current level of expected returns on risk-free investments comprised of government bonds, the historical level of the risk premium associated with the other asset classes in which the portfolio is invested, and the expectations for future returns for each asset class. The expected return for each asset class was then weighted based on the target asset allocation to develop the expected long-term rate of return for each plan.

Cabot’s investment strategy for each of its defined benefit plans in the U.S. and abroad is generally based on a set of investment objectives and policies that cover time horizons and risk tolerance levels consistent with plan liabilities. Periodic studies are performed to determine the asset mix that will meet pension obligations at a reasonable cost to the Company. The assets of the defined benefit plans are comprised principally of investments in equity and high quality fixed income securities, which are broadly diversified across the capitalization and style spectrum and are managed using both active and passive strategies. The weighted average target asset allocation for the U.S. plans is 32% in cash equivalents and 68% in fixed income and for the foreign plans is 41%

in equity, 49% in fixed income, 6% in real estate and 4% in cash and other securities. The target allocation of the U.S. Pension plan has changed as a result of the anticipated plan settlement discussed in the U.S. Plan Termination section above.

For pension plan assets classified as Level 1 measurements (measured using quoted prices in active markets), total fair value is either the price of the most recent trade at the time of the market close or the official close price, as defined by the exchange on which the asset is most actively traded on the last trading day of the period, multiplied by the number of units held without consideration of transaction costs.

For pension plan assets classified as Level 2 measurements, where the security is frequently traded in less active markets, fair value is based on the closing price at the end of the period; where the security is less frequently traded, fair value is based on the price a dealer would pay for the security or similar securities, adjusted for any terms specific to that asset or liability. Market inputs are obtained from well-established and recognized vendors of market data and subjected to tolerance/quality checks.

The fair value of the Company’s pension plan assets at September 30, 2019 and 2018 by asset category is as follows:

	September 30
	2019						2018
	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Observable Inputs (Level 2)		Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Observable Inputs (Level 2)		Total
	(In millions)
Cash	$	2	$	—	$	2	$	3	$	—	$	3
Direct investments:
U.S government bonds		—		—		—		17		13		30
U.S. corporate bonds		—		—		—		—		74		74
Non-U.S. equities		3		—		3		—		—		—
Non-U.S. government bonds		2		—		2		—		—		—
Non-U.S. corporate bonds		3		—		3		—		—		—
Mortgage backed securities		—		1		1		—		—		—
Other fixed income		1		—		1		—		—		—
Total direct investments		9		1		10		17		87		104
Investment funds:
Equity funds⁽¹⁾		—		74		74		44		126		170
Fixed income funds⁽²⁾		104		90		194		—		169		169
Real estate funds⁽³⁾		—		12		12		—		9		9
Cash equivalent funds		48		—		48		1		—		1
Total investment funds		152		176		328		45		304		349
Alternative investments:
Insurance contracts⁽⁴⁾		—		5		5		—		16		16
Other alternative investments		1		—		1		—		—		—
Total alternative investments		1		5		6		—		16		16
Total pension plan assets	$	164	$	182	$	346	$	65	$	407	$	472

⁽¹⁾	The equity funds asset class includes funds that invest in U.S. equities as well as equity securities issued by companies incorporated, listed or domiciled in countries in developed and/or emerging markets. These companies may be in the small-, mid- or large-cap categories.

⁽²⁾

The fixed income funds asset class includes investments in high quality funds. High quality fixed income funds primarily invest in low risk U.S. and non-U.S. government securities, investment-grade corporate bonds, mortgages and asset-backed securities. A significant portion of the fixed income funds include investment in long-term bond funds.

⁽³⁾

The real estate funds asset class includes funds that primarily invest in entities which are principally engaged in the ownership, acquisition, development, financing, sale and/or management of income-producing real estate properties, both commercial and residential. These funds typically seek long-term growth of capital and current income that is above average relative to public equity funds.

⁽⁴⁾	Insurance contracts held by the Company’s non-U.S. plans are issued by well-known, highly rated insurance companies.

Stock-Based Compensation

12 Months Ended

Sep. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

Note O. Stock-Based Compensation

The Company has established equity compensation plans that provide stock-based compensation to eligible employees. The 2009 Long-Term Incentive Plan (the “2009 Plan”) authorized the issuance of up to 8,854,000 shares of common stock. The 2017 Long-Term Incentive Plan (the “2017 Plan”) was approved by Cabot’s stockholders on March 9, 2017 and authorizes the issuance of up to 5,375,000 shares of common stock. The Company ceased granting awards under the 2009 Plan when the 2017 Plan was approved and, accordingly, the 2017 Plan is the only equity incentive plan under which the Company may grant equity awards to employees.

The terms of awards made under Cabot’s equity compensation plans are generally determined by the Compensation Committee of Cabot’s Board of Directors. The awards made in fiscal 2019, 2018 and 2017 consist of grants of stock options, time-based restricted stock units, and performance-based restricted stock units. The options were issued with an exercise price equal to 100% of the market price of Cabot’s common stock on the date of grant, generally vest over a three year period (30% on each of the first and second anniversaries of the date of grant and 40% on the third anniversary of the date of grant) and have a ten-year term. The restricted stock units generally vest three years from the date of the grant. The number of shares issuable, if any, when a performance-based restricted stock unit award vests will depend on the degree of achievement of the corporate performance metrics for each year within the three-year performance period of the award. Accordingly, future compensation costs associated with outstanding awards of performance-based restricted stock units may increase or decrease based on the probability of the Company achieving the performance metrics.

Stock-based employee compensation expense was $8 million, $16 million and $10 million, after tax, for fiscal 2019, 2018 and 2017, respectively.

The Company recognized the full impact of its stock-based employee compensation expense in the Consolidated Statements of Operations for fiscal 2019, 2018 and 2017 and did not capitalize any such costs on the Consolidated Balance Sheets because those that qualified for capitalization were not material. The following table presents stock-based compensation expenses included in the Company’s Consolidated Statements of Operations:

	Years Ended September 30
	2019			2018			2017
	(In millions)
Cost of sales	$	1		$	2		$	1
Selling and administrative expenses		9			19			14
Research and technical expenses		1			1			1
Stock-based compensation expense		11			22			16
Income tax benefit		(3	)		(6	)		(6	)
Net stock-based compensation expense	$	8		$	16		$	10

As of September 30, 2019, Cabot has $16 million and $2 million of total unrecognized compensation cost related to restricted stock units and options, respectively, granted under the Company’s equity incentive plans. These costs are expected to be recognized over a weighted-average period of approximately one year for restricted stock units and options.

Equity Incentive Plan Activity

The following table summarizes the total stock option and restricted stock unit activity in the equity incentive plans for fiscal 2019:

	Stock Options							Restricted Stock Units
	Total Options ⁽⁴⁾			Weighted Average Exercise Price		Weighted Average Grant Date Fair Value		Restricted Stock Units⁽¹⁾			Weighted Average Grant Date Fair Value
	(Shares in thousands)
Outstanding at September 30, 2018		881		$	50.73	$	13.82		985		$	50.16
Granted		343		$	49.70	$	10.85		316		$	49.44
Performance-based adjustment⁽²⁾		—		$	—	$	—		10		$	62.98
Exercised / Vested		(49	)	$	35.06	$	9.41		(383	)	$	40.97
Cancelled / Forfeited		(153	)	$	54.44	$	10.36		(163	)	$	54.48
Outstanding at September 30, 2019⁽³⁾		1,022		$	50.57	$	12.13		765		$	53.71
Exercisable at September 30, 2019		499		$	48.09

⁽¹⁾	The number granted represents the number of shares issuable upon vesting of time-based restricted stock units and performance-based restricted stock units, assuming the Company performs at the target performance level in each year of the three-year performance period.

⁽²⁾	Represents the net incremental number of shares issuable upon vesting of performance-based restricted stock units based upon the achievement of the annual financial performance metrics for fiscal 2019.

⁽³⁾	Stock options outstanding include options vested and expected to vest in the future and have a weighted average remaining contractual life of 6.74 years.

⁽⁴⁾	Unvested stock options were approximately 523,000 and 546,000 at September 30, 2019 and 2018 and their weighted average grant date fair values were $52.95 and $54.48, respectively.

Stock Options

The aggregate intrinsic value for all options outstanding and options exercisable was nil since the Company’s closing stock price of $45.32 at September 30, 2019 was below their weighted average exercise price. The intrinsic value of options exercised during fiscal 2019, 2018 and 2017 was $1 million, $11 million and $16 million, respectively, and the Company received cash of $2 million, $22 million and $21 million, respectively, from these exercises. In fiscal 2019 and 2018, the Company recognized an immaterial tax expense and a $1 million tax benefit, respectively, from the exercise of stock options, which is included in (Provision) benefit for income taxes within the Consolidated Statement of Operations. Prior to the Company’s adoption of the new accounting standard for stock compensation in fiscal 2018, tax benefits associated with stock option exercises were included in APIC.

The Company uses the Black-Scholes option-pricing model to estimate the fair value of the options at the grant date. The weighted average grant date fair values of options granted during fiscal 2019, 2018 and 2017 was $10.85, $15.21, and $12.76 per option, respectively. The fair values on the grant date were calculated using the following weighted-average assumptions:

	Years Ended September 30
	2019			2018			2017
Expected stock price volatility		27	%		28	%		32	%
Risk free interest rate		3.1	%		2.2	%		1.8	%
Expected life of options (years)		6			6			6
Expected annual dividends per year	$	1.32		$	1.26		$	1.20

The expected stock price volatility assumption was determined using the historical volatility of the Company’s common stock over the expected life of the option. The expected term reflects the anticipated time period between the measurement date and the exercise date or post-vesting cancellation date.

Restricted Stock Units

The value of restricted stock unit awards is the closing stock price at the date of the grant. The weighted average grant date fair values of restricted stock unit awards granted during fiscal 2019, 2018 and 2017 was $49.44, $62.18, and $51.03, respectively. The intrinsic value of restricted stock units (meaning the fair value of the units on the date of vesting) that vested during fiscal 2019, 2018 and 2017 was $18 million, $12 million and $7 million, respectively.

Supplemental 401(k) Plan

Cabot’s Deferred Compensation and Supplemental Retirement Plan (“SERP 401(k)”) provides benefits to highly compensated employees when the retirement plan limits established under the Internal Revenue Code prevent them from receiving all of the Company matching and retirement contributions that would otherwise be provided under the qualified 401(k) plan. The SERP 401(k) is non-qualified and unfunded. Contributions under the SERP 401(k) are treated as if invested in Cabot common stock. The majority of the distributions made under the SERP 401(k) are required to be paid with shares of Cabot common stock. The remaining distributions, which relate to certain grandfathered accounts, will be paid in cash based on the market price of Cabot common stock at the time of distribution. The aggregate value of the accounts that will be paid out in stock, which is equivalent to approximately 93,000 and 116,000 shares of Cabot common stock as of September 30, 2019 and 2018, respectively, is reflected at historic cost in stockholders’ equity, and the aggregate value of the accounts that will be paid in cash, which is $1 million as of both September 30, 2019 and 2018, is reflected in other long-term liabilities and marked-to-market quarterly.

Restructuring

12 Months Ended

Sep. 30, 2019

Restructuring And Related Activities [Abstract]

Restructuring

Note P. Restructuring

Cabot’s restructuring activities were recorded in the Consolidated Statements of Operations as follows:

	Years Ended September 30
	2019		2018			2017
	(In millions)
Cost of sales	$	9	$	(31	)	$	2
Selling and administrative expenses		7		1			1
Total	$	16	$	(30	)	$	3

Details of all restructuring activities and the related reserves for fiscal 2017, 2018, and 2019 were as follows:

	Severance and Employee Benefits			Environmental Remediation and Decommissioning Activities			Non-Cash Asset Impairment and Accelerated Depreciation			Asset Sales			Other			Total
	(In millions)
Reserve at September 30, 2016	$	3		$	2		$	—		$	—		$	—		$	5
Charges (gain)		1			1			—			—			1			3
Costs charged against assets		—			—			—			—			1			1
Cash (paid) received		(3	)		(1	)		—			—			(2	)		(6	)
Reserve at September 30, 2017		1			2			—			—			—			3
Charges (gain)		2			3			1			(38	)		2			(30	)
Costs charged against liabilities		—			—			(1	)		(1	)		—			(2	)
Cash paid		(2	)		(1	)		—			39			(2	)		34
Reserve at September 30, 2018		1			4			—			—			—			5
Charges (gain)		11			—			2			—			3			16
Costs charged against assets		—			—			(2	)		—			—			(2	)
Cash (paid) received		(9	)		—			—			—			(3	)		(12	)
Reserve at September 30, 2019	$	3		$	4		$	—		$	—		$	—		$	7

Cabot’s severance and employee benefit reserves and other closure related reserves are reflected in Accounts payable and accrued liabilities on the Company’s Consolidated Balance Sheets. Cabot’s environmental remediation reserves related to restructuring activities are reflected in Other liabilities on the Company’s Consolidated Balance Sheets.

Purification Solutions Transformation Plan

In December 2018, the Company began implementation of a transformation plan to improve the long-term performance of the Purification Solutions segment. The purpose of the plan is to focus the business’s product portfolio, optimize its manufacturing assets, and streamline its organizational structure to support the new focus. The Company recorded charges of approximately $9 million related to this plan in the year ended September 30, 2019, comprised of approximately $8 million of severance costs and $1 million of professional fees and other charges. The Company expects to record cash charges of approximately $1 million in fiscal 2020 for additional restructuring charges related to this plan. Cabot paid approximately $8 million related to these activities in the year ended September 30, 2019, and expects to pay approximately $2 million in fiscal 2020. As of September 30, 2019, Cabot had $1 million of accrued severance charges in the Consolidated Balance Sheets related to these actions.

Sale of Land Rights in Thane, India

During fiscal 2018, Cabot entered into a binding memorandum of understanding to sell its land rights in Thane, India for approximately $28 million. The Company received a deposit of $3 million in cash in the first quarter of fiscal 2016, an additional deposit of $3 million in cash in the third quarter of fiscal 2018, and the final balance of $22 million was received on September 14, 2018. Based on the execution of the binding agreement and non-refundable receipt of cash, the Company has recorded the pre-tax gain on sale of $28 million to Cost of sales in the Consolidated Statements of Operations in the year ended September 30, 2018.

2016 Plan

As part the Company’s 2016 restructuring plan, the Company ceased operations at its carbon black manufacturing facility in Merak, Indonesia in January 2016 and completed the sale of the land on which the facility was located in the second quarter of fiscal 2018 for cash consideration totaling approximately $13 million, resulting in a net pre-tax gain of approximately $11 million recorded to Cost of sales in the Company’s Consolidated Statements of Operations.

Accumulated Other Comprehensive Income (Loss)

12 Months Ended

Sep. 30, 2019

Stockholders Equity Note [Abstract]

Accumulated Other Comprehensive Income (Loss)

Note Q. Accumulated Other Comprehensive Income (Loss)

Changes in each component of AOCI, net of tax, are as follows for fiscal 2018 and 2019:

	Currency Translation Adjustment			Unrealized Gains on Investment			Pension and Other Postretirement Benefit Liability Adjustment			Total
	(In millions)
Balance at September 30, 2017 attributable to Cabot Corporation	$	(204	)	$	2		$	(57	)	$	(259	)
Other comprehensive income (loss) before reclassifications		(64	)		(1	)		6			(59	)
Amounts reclassified from AOCI		(2	)		—			(1	)		(3	)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		(4	)		—			—			(4	)
Balance at September 30, 2018 attributable to Cabot Corporation		(266	)		1			(52	)		(317	)
Other comprehensive income (loss) before reclassifications		(69	)		—			4			(65	)
Amounts reclassified from AOCI		(9	)		—			(6	)		(15	)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		(6	)		—			—			(6	)
Balance at September 30, 2019 attributable to Cabot Corporation	$	(338	)	$	1		$	(54	)	$	(391	)

The amounts reclassified out of AOCI and into the Consolidated Statements of Operations for the fiscal years ended September 30, 2019, 2018 and 2017 are as follows:

	Affected Line Item in the Consolidated	Years Ended September 30
	Statements of Operations	2019			2018			2017
		(In Millions)
Derivatives: net investment hedges
(Gains) losses reclassified to interest expense	Interest expense	$	(5	)	$	(5	)	$	—
(Gains) losses excluded from effectiveness testing and amortized to interest expense	Interest expense		1			2			—
Pension and other postretirement benefit liability adjustment
Amortization of actuarial losses	Net Periodic Benefit Cost - see Note N for details		1			2			5
Amortization of prior service cost (credit)	Net Periodic Benefit Cost - see Note N for details		—			(3	)		(3	)
Settlement and curtailment gain	Net Periodic Benefit Cost - see Note N for details		(7	)		—			—
Specialty Fluids divestiture	Specialty Fluids loss on sale and asset impairment - see Note D for details		(3	)		—			—
Total before tax			(13	)		(4	)		2
Tax impact	Provision (benefit) for income taxes		(2	)		1			—
Total after tax		$	(15	)	$	(3	)	$	2

Earnings Per Share

12 Months Ended

Sep. 30, 2019

Earnings Per Share [Abstract]

Earnings Per Share

Note R. Earnings Per Share

The following tables summarize the components of the basic and diluted earnings per common share (“EPS”) computations:

	Years Ended September 30
	2019		2018			2017
	(In millions, except per share amounts)
Basic EPS:
Net income (loss) attributable to Cabot Corporation	$	157	$	(113	)	$	248
Less: Dividends and dividend equivalents to participating securities		1		1			—
Less: Undistributed earnings allocated to participating securities⁽¹⁾		1		—			2
Earnings (loss) allocated to common shareholders (numerator)	$	155	$	(114	)	$	246

Weighted average common shares and participating securities outstanding		59.5		62.4			62.8
Less: Participating securities⁽¹⁾		0.8		0.7			0.5
Adjusted weighted average common shares (denominator)		58.7		61.7			62.3

Per share amounts—basic:
Net income (loss) attributable to Cabot Corporation	$	2.64	$	(1.85	)	$	3.94

Diluted EPS:
Earnings (loss) allocated to common shareholders	$	155	$	(114	)	$	246
Plus: Earnings (loss) allocated to participating securities		2		—			2
Less: Adjusted earnings allocated to participating securities⁽²⁾		2		—			2
Earnings (loss) available to common shares (numerator)	$	155	$	(114	)	$	246

Adjusted weighted average common shares outstanding		58.7		61.7			62.3
Effect of dilutive securities:
Common shares issuable⁽³⁾		0.1		—			0.4
Adjusted weighted average common shares (denominator)		58.8		61.7			62.7

Per share amounts—diluted:
Net income (loss) attributable to Cabot Corporation	$	2.63	$	(1.85	)	$	3.91

⁽¹⁾

^{Participating securities consist of shares underlying outstanding and achieved performance-based restricted stock units issued during and after fiscal 2017 and all unvested time-based restricted stock units. The holders of these units are entitled to receive dividend equivalents payable in cash to the extent dividends are paid on the Company’s outstanding common stock and equal in value to the dividends that would have been paid in respect of the shares underlying such units.}

Undistributed earnings are the earnings which remain after dividends declared during the period are assumed to be distributed to the common and participating shareholders. Undistributed earnings are allocated to common and participating shareholders on the same basis as dividend distributions. The calculation of undistributed earnings is as follows:

	Years Ended September 30
	2019		2018			2017
	(In millions)
Calculation of undistributed earnings:
Net income (loss) attributable to Cabot Corporation	$	157	$	(113	)	$	248
Less: Dividends declared on common stock		80		79			77
Less: Dividends and dividend equivalents to participating securities		1		1			—
Undistributed earnings (loss)	$	76	$	(193	)	$	171
Allocation of undistributed earnings:
Undistributed earnings (loss) allocated to common shareholders	$	75	$	(193	)	$	169
Undistributed earnings allocated to participating securities		1		—			2
Undistributed earnings (loss)	$	76	$	(193	)	$	171

⁽²⁾	^{Undistributed earnings (loss) are adjusted for the assumed distribution of dividends to the dilutive securities, which are described in (3) below, and then reallocated to participating securities.}

⁽³⁾

^{Represents incremental shares of common stock from the (i) assumed exercise of stock options issued under Cabot’s equity incentive plans; (ii) assumed issuance of shares to employees pursuant to the Company’s SERP 401(k) Plan; and (iii) assumed issuance of shares for outstanding and achieved performance-based stock unit awards issued before fiscal 2017 under Cabot’s equity incentive plans using the treasury stock method. For fiscal 2019, 2018 and 2017, respectively, 942,060, 229,220 and 179,052 incremental shares of common stock were not included in the calculation of diluted earnings per share because the inclusion of these shares would have been antidilutive.}

Income Taxes

12 Months Ended

Sep. 30, 2019

Income Tax Disclosure [Abstract]

Income Taxes

Note S. Income Taxes

Income from continuing operations before income taxes and equity in net earnings of affiliated companies was as follows:

	Years Ended September 30
	2019			2018			2017
	(In millions)
Domestic	$	(66	)	$	(229	)	$	(8	)
Foreign		321			346			307
Income from continuing operations before income taxes and equity in earnings of affiliated companies	$	255		$	117		$	299

Tax provision (benefit) for income taxes consisted of the following:

	Years Ended September 30
	2019			2018			2017
	(In millions)
U.S. federal and state:
Current	$	2		$	14		$	5
Deferred		(30	)		114			(26	)
Total		(28	)		128			(21	)
Foreign:
Current		95			88			59
Deferred		3			(23	)		(5	)
Total		98			65			54
Provision (benefit) for income taxes	$	70		$	193		$	33

The provision (benefit) for income taxes differed from the provision for income taxes as calculated using the U.S. statutory rate as follows:

	Years Ended September 30
	2019			2018			2017
	(In millions)
Computed tax expense at the federal statutory rate	$	53		$	29		$	105
Foreign income:
Impact of taxation at different rates, repatriation, losses and other		42			6			(75	)
Impact of increase (decrease) in valuation allowance on deferred taxes		(25	)		(16	)		(7	)
Impact of foreign losses for which a current tax benefit is not available		—			—			1
Impact of non-deductible net currency losses		—			2			—
Impact of the Tax Cuts and Jobs Act of 2017		—			159			—
Global Intangible Low Taxed Income (GILTI)		10			—			—
U.S. and state benefits from research and experimentation activities		(2	)		(2	)		(2	)
Provision (settlement) of unrecognized tax benefits		(8	)		1			7
Impact of goodwill impairment charge		—			18			—
Permanent differences, net		1			(1	)		5
State taxes, net of federal effect		(1	)		(3	)		(1	)
Provision (benefit) for income taxes	$	70		$	193		$	33

In the fiscal 2019 tax provision, Cabot recorded $7 million of net discrete tax benefit composed of tax benefits of $4 million related to uncertain tax positions, $2 million related to a pension settlement, $2 million related to changes in valuation allowance on beginning of year tax balances, $2 million related to the Specialty Fluids sale, $1 million related to result of changes in non-US tax laws and $1 million related to other miscellaneous tax items, partially offset by net tax charges of $5 million related to various return to provision adjustments related to tax return filings and audit settlements.

In the fiscal 2018 tax provision, Cabot recorded $120 million of net discrete tax expense, composed of $159 million net tax impact of the Act and $3 million tax expense upon the sale of assets, offset by net tax benefits of $29 million related to impairment and $15 million from a change in valuation allowance on a beginning of year tax balance, and net tax charge of $2 million related to other miscellaneous tax items.

In the fiscal 2017 tax provision, Cabot recorded $25 million of net discrete tax benefits, composed of net tax benefits of $16 million associated with the generation of excess foreign tax credits upon repatriation of previously taxed foreign earnings and the accrual of U.S. tax on certain foreign earnings, a net tax benefit of $6 million from a change in valuation allowance on a beginning of year tax balance, net tax benefits of $4 million for various return to provision adjustments related to tax return filings and net tax charges of $1 million related to other miscellaneous tax items.

Tax Reform

On December 22, 2017, the U.S. enacted significant changes to federal income tax law affecting the Company, including a permanent reduction of the U.S. corporate income tax rate from 35% to 21%, effective January 1, 2018, as well as a 100% dividend received deduction for foreign dividends. Although the passage of the Act reduced the U.S. tax rate and effectively created a participation exemption regime for foreign earnings, there are certain other aspects of the new legislation that affect the Company, including in particular, immediate U.S. taxation of global intangible low-taxed income (“GILTI”) earned by foreign subsidiaries. GILTI earned by Controlled Foreign Corporations (“CFCs”) must be included currently in the gross income of the CFCs’ U.S. shareholder. GILTI is the excess of the shareholder’s “net CFC-tested income” over the net deemed tangible income return, which is currently defined as the excess of (1) 10% of the aggregate of the U.S. shareholder’s pro rata share of the qualified business asset investment of each CFC with respect to which it is a U.S. shareholder over (2) the amount of certain interest expense taken into account in the determination of net CFC-tested income. GILTI had a negative impact on earnings of $10 million and this is the primary driver of the increase in the Company’s effective tax rate. In transitioning to this participation exemption regime, the Company was also subject, during fiscal 2018, to a one-time tax on the deemed repatriation of certain foreign earnings. The Company did not incur a Base Erosion Anti-Abuse Tax (“BEAT”) liability in fiscal 2019 since it did not exceed the base erosion percentage of 3% for the taxable year. A significant portion of the Company’s intercompany payments were exempted from BEAT. The Company will continue to analyze the applicability of the BEAT provisions on a quarterly basis.

In January 2018, accounting guidance was issued requiring a company to make an accounting policy to either treat taxes due on future U.S. inclusions in taxable income related to GILTI as a current-period expense when incurred (the "period cost method") or factor such amounts into a company’s measurement of its deferred taxes (the "deferred method"). The Company has elected the period cost method and has considered the estimated 2019 GILTI impact in its 2019 tax expense.

Significant components of deferred income taxes were as follows:

	September 30
	2019			2018
	(In millions)
Deferred tax assets:
Deferred expenses	$	15		$	17
Intangible assets		28			23
Inventory		9			4
Other		3			4
Pension and other benefits		41			45
Net operating loss carryforwards		124			146
Foreign tax credit carryforwards		20			12
R&D credit carryforwards		43			41
Other business credit carryforwards		29			39
Subtotal		312			331
Valuation allowance		(124	)		(169	)
Total deferred tax assets	$	188		$	162

	September 30
	2019			2018
	(In millions)
Deferred tax liabilities:
Property, plant and equipment	$	(61	)	$	(56	)
Unremitted earnings of non-U.S. subsidiaries		(5	)		(14	)
Total deferred tax liabilities	$	(66	)	$	(70	)

Approximately $711 million of net operating loss carryforwards (“NOLs”) and $99 million of other tax credit carryforwards remain at September 30, 2019. The benefits of these carryforwards are dependent upon taxable income during the carryforward period in the jurisdictions in which they arose. Accordingly, a valuation allowance has been provided where management has determined that it is more likely than not that the carryforwards will not be utilized. The following table provides detail surrounding the expiration dates of these carryforwards:

Years Ending September 30	NOLs		Credits
	(In millions)
2020 - 2026	$	262	$	40
2027 and thereafter		168		57
Indefinite carryforwards		281		2
Total	$	711	$	99

As of September 30, 2019, provisions have not been made for non-U.S. withholding taxes or other applicable taxes on approximately $1,316 million of undistributed earnings of non-U.S. subsidiaries, as these earnings are considered indefinitely reinvested. Cabot continually reviews the financial position and forecasted cash flows of its U.S. consolidated group and foreign subsidiaries in order to reaffirm the Company’s intent and ability to continue to indefinitely reinvest earnings of its foreign subsidiaries or whether such earnings will need to be repatriated in the foreseeable future. Such review encompasses operational needs and future capital investments. From time to time, however, the Company’s intentions relative to specific indefinitely reinvested amounts change because of certain unique circumstances. These earnings could become subject to non-U.S. withholding taxes and other applicable taxes if they were remitted to the U.S.

As of September 30, 2019, the Company had U.S. net deferred tax assets of $127 million, including $20 million of foreign tax credit carryforwards. Management believes that the Company’s history of generating domestic profits, defined as U.S. income from continuing operations adjusted for U.S. permanent differences, provides adequate evidence that it is more likely than not that all of the U.S. net deferred tax assets will be realized in the normal course of business. Realization of deferred tax assets is dependent upon future taxable income generated over an extended period of time.

As of September 30, 2019, the Company needs to generate approximately $606 million in cumulative future U.S. taxable income at various times over approximately 20 years to realize all of its net U.S. deferred tax assets. The Company reviews its forecast in relation to actual results and expected trends on a quarterly basis. Failure to achieve operating income targets may change the Company’s assessment regarding the realization of Cabot’s deferred tax assets and such change could result in a valuation allowance being recorded against some or all of the Company’s deferred tax assets. Any increase in a valuation allowance would result in additional income tax expense, lower stockholders’ equity and could have a significant impact on Cabot’s earnings in future periods.

The valuation allowances at September 30, 2019 and 2018 represent management’s best estimate of the non-realizable portion of the deferred tax assets. The valuation allowance decreased by $45 million in fiscal 2019 primarily due to the release of valuation allowance from the expiration of net operating losses in certain jurisdictions and the divestiture of the Company’s Specialty Fluids business of $16 million. The valuation allowance increased by $1 million in fiscal 2018 due to net reductions in value of certain pre-existing and acquired future tax benefits and net operating losses generated that are included in deferred tax assets.

Cabot has filed its tax returns in accordance with the tax laws in each jurisdiction and recognizes tax benefits for uncertain tax positions when the position would more likely than not be sustained based on its technical merits and recognizes measurement adjustments when needed. As of September 30, 2019, the total amount of unrecognized tax benefits was $27 million, of which $17 million was recorded in the Company’s Consolidated Balance Sheets and $10 million of deferred tax assets, principally related to state net operating loss carryforwards, have not been recorded. In addition, accruals of less than $1 million and $7 million have been recorded for penalties and interest, respectively, as of September 30, 2019, and $1 million and $9 million, respectively, as of September 30, 2018. Total penalties and interest recorded in the tax provision in the Consolidated Statements of Operations was $2 million in each of the years ended September 30, 2019, 2018 and 2017. If the unrecognized tax benefits were recognized at a given point in time, there would be approximately $27 million favorable impact on the Company’s tax provision before consideration of the impact of the potential need for valuation allowances.

A reconciliation of the beginning and ending amount of unrecognized tax benefits for fiscal years 2019, 2018 and 2017 is as follows:

	Years Ended September 30
	2019			2018			2017
	(In millions)
Balance at beginning of the year	$	37		$	36		$	30
Additions based on tax provisions related to the current year		—			2			2
Additions for tax positions of prior years		—			1			8
Reductions of tax provisions of prior years		(1	)		—			(1	)
Reductions related to settlements		(5	)		—			(2	)
Reductions from lapse of statute of limitations		(4	)		(2	)		(1	)
Balance at end of the year	$	27		$	37		$	36

Cabot and certain subsidiaries are under audit in a number of jurisdictions. In addition, certain statutes of limitations are scheduled to expire in the near future. It is reasonably possible that a further change in the unrecognized tax benefits may occur within the next twelve months related to the settlement of one or more of these audits or the lapse of applicable statutes of limitations; however, an estimated range of the impact on the unrecognized tax benefits cannot be quantified at this time.

Cabot files U.S. federal and state and non-U.S. income tax returns in jurisdictions with varying statutes of limitations. The 2016 through 2018 tax years generally remain subject to examination by the IRS and various tax years from 2005 through 2018 remain subject to examination by the respective state tax authorities. In significant non-U.S. jurisdictions, various tax years from 2003 through 2018 remain subject to examination by their respective tax authorities. As of September 30, 2019, Cabot’s significant non-U.S. jurisdictions include Canada, China, France, Germany, Italy, Japan, and the Netherlands.

Commitments and Contingencies

12 Months Ended

Sep. 30, 2019

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note T. Commitments and Contingencies

Operating Lease Commitments

Cabot leases certain transportation vehicles, warehouse facilities, office space, machinery and equipment under cancelable and non-cancelable operating leases, most of which expire within ten years and may be renewed by Cabot. Escalation clauses, lease payments dependent on existing rates/indexes and other lease incentives are included in the minimum lease payments and such lease payments are recognized on a straight-line basis over the minimum lease term. Rent expense under such arrangements for fiscal 2019, 2018 and 2017 totaled $27 million, $32 million and $33 million, respectively. Future minimum rental commitments under non-cancelable leases are as follows:

Years Ending September 30	(In millions)
2020	$	23
2021		14
2022		9
2023		9
2024		8
2025 and thereafter		68
Total future minimum rental commitments	$	131

Other Long-Term Commitments

Cabot has entered into long-term purchase agreements primarily for the purchase of raw materials. Under certain of these agreements, the quantity of material being purchased is fixed, but the price paid changes as market prices change. Raw materials purchased under these agreements by segment for fiscal 2019, 2018 and 2017 are as follows:

	Years Ended September 30
	2019		2018		2017
	(In millions)
Reinforcement Materials	$	393	$	375	$	281
Performance Chemicals		65		55		43
Purification Solutions		8		11		7
Total	$	466	$	441	$	331

Included in the table above are raw materials purchases from noncontrolling shareholders of consolidated subsidiaries. These purchases were $156 million during both fiscal 2019 and fiscal 2018 and $116 million during fiscal 2017, and accounts payable and accrued liabilities owed to noncontrolling shareholders as of September 30, 2019 and 2018, were $20 million and $8 million, respectively.

For these purchase commitments, the amounts included in the table below are based on market prices as of September 30, 2019 which may differ from actual market prices at the time of purchase.

	Payments Due by Fiscal Year
	2020		2021		2022		2023		2024		Thereafter		Total
	(In millions)
Reinforcement Materials	$	218	$	123	$	116	$	108	$	107	$	1,246	$	1,918
Performance Chemicals		57		55		53		35		30		402	$	632
Purification Solutions		6		1		—		—		—		—		7
Total	$	281	$	179	$	169	$	143	$	137	$	1,648	$	2,557

The Company has also entered into long-term purchase agreements primarily for services related to information technology, which are not included in the table above, that total $12 million as of September 30, 2019, the majority of which is expected to be paid within the next 5 years.

Guarantee Agreements

Cabot has provided certain indemnities pursuant to which it may be required to make payments to an indemnified party in connection with certain transactions and agreements. In connection with certain acquisitions and divestitures, Cabot has provided routine indemnities with respect to such matters as environmental, tax, insurance, product and employee liabilities. In connection with various other agreements, including service and supply agreements with customers, Cabot has provided indemnities for certain contingencies and routine warranties. Cabot is unable to estimate the maximum potential liability for these types of indemnities as a maximum obligation is not explicitly stated in most cases and the amounts, if any, are dependent upon the outcome of future contingent events, the nature and likelihood of which cannot be reasonably estimated. The duration of the indemnities vary, and in many cases are indefinite. Cabot has not recorded any liability for these indemnities in the consolidated financial statements, except as otherwise disclosed.

Self-Insurance and Retention for Certain Contingencies

The Company is partially self-insured for certain third-party liabilities globally, as well as workers’ compensation and employee medical benefits in the United States. The third-party and workers’ compensation liabilities are managed through a wholly-owned insurance captive and the related liabilities are included in the consolidated financial statements. The employee medical obligations are managed by a third-party provider and the related liabilities are included in the consolidated financial statements. To limit Cabot’s potential liabilities for these risks, however, the Company purchases insurance from third-parties that provides stop-loss protection. The self-insured liability in fiscal 2019 for third-party liabilities was $500,000 per accident for auto, $2 million per occurrence for all other, $1 million per accident for U.S. workers’ compensation, and the retention for medical costs in the United States is at most $250,000 per person per annum.

Contingencies

Cabot is a defendant, or potentially responsible party, in various lawsuits and environmental proceedings wherein substantial amounts are claimed or at issue.

Environmental Matters

As of September 30, 2019 and 2018, Cabot had $13 million and $15 million, respectively, reserved for environmental matters. These environmental matters mainly relate to former operations. The Company’s reserves for environmental matters represent Cabot’s best estimates of the probable costs to be incurred at those sites where costs are reasonably estimable based on the Company’s analysis of the extent of clean up required, alternative clean-up methods available, abilities of other responsible parties to contribute and its interpretation of laws and regulations applicable to each site. In fiscal 2019 and 2018, there was $9 million and $12 million, respectively, in Accounts payable and accrued liabilities in the Consolidated Balance Sheets for environmental matters. In fiscal 2019 and 2018, there was $4 million and $3 million, respectively in Other liabilities in the Consolidated Balance Sheets for environmental matters. Cabot reviews the adequacy of the reserves as circumstances change at individual sites and adjusts the reserves as appropriate. Almost all of Cabot’s environmental issues relate to sites that are mature and have been investigated and studied and, in many cases, are subject to agreed upon remediation plans. However, depending on the results of future testing, changes in risk assessment practices, remediation techniques and regulatory requirements, newly discovered conditions, and other factors, it is reasonably possible that the Company could incur additional costs in excess of environmental reserves currently recorded. Management estimates, based on the latest available information, that any such future environmental remediation costs that are reasonably possible to be in excess of amounts already recorded would be immaterial to the Company’s consolidated financial statements.

Charges for environmental expense were less than $1 million in fiscal 2019, $6 million in fiscal 2018 and less than $1 million in fiscal 2017, and are included in Cost of sales in the Consolidated Statements of Operations. Cash payments related to these environmental matters were $2 million in fiscal 2019, $3 million in fiscal 2018 and $2 million in fiscal 2017. The Company anticipates that expenditures related to these environmental matters will be made over a number of years.

The operation and maintenance component of the $13 million reserve for environmental matters was $4 million at September 30, 2019.

In November 2013, Cabot entered into a Consent Decree with the EPA and the Louisiana Department of Environmental Quality (“LDEQ”) regarding Cabot’s three carbon black manufacturing facilities in the U.S. This settlement is related to EPA’s national enforcement initiative focused on the U.S. carbon black manufacturing sector alleging non-compliance with certain regulatory and permitting requirements under The Clean Air Act, including the New Source Review (“NSR”) construction permitting requirements. Pursuant to this settlement, Cabot is in the process of installing technology controls for the reduction of sulfur dioxide and nitrogen oxide emissions at certain of its carbon black plants.

Respirator Liabilities

Cabot has exposure in connection with a safety respiratory products business that a subsidiary acquired from American Optical Corporation (“AO”) in an April 1990 asset purchase transaction. The subsidiary manufactured respirators under the AO brand and disposed of that business in July 1995. In connection with its acquisition of the business, the subsidiary agreed, in certain circumstances, to assume a portion of AO’s liabilities, including costs of legal fees together with amounts paid in settlements and judgments, allocable to AO respiratory products used prior to the 1990 purchase by the Cabot subsidiary. In exchange for the subsidiary’s assumption of certain of AO’s respirator liabilities, AO agreed to provide to the subsidiary the benefits of: (i) AO’s insurance coverage for the period prior to the 1990 acquisition and (ii) a former owner’s indemnity of AO holding it harmless from any liability allocable to AO respiratory products used prior to May 1982.

Generally, these respirator liabilities involve claims for personal injury, including asbestosis, silicosis and coal worker’s pneumoconiosis, allegedly resulting from the use of respirators that are alleged to have been negligently designed and/or labeled. Neither Cabot, nor its past or present subsidiaries, at any time manufactured asbestos or asbestos-containing products. At no time did this respiratory product line represent a significant portion of the respirator market.

The subsidiary transferred the business to Aearo Corporation (“Aearo”) in July 1995. Cabot agreed to have the subsidiary retain certain liabilities associated with exposure to asbestos and silica while using respirators prior to the 1995 transaction so long as Aearo paid, and continues to pay, Cabot an annual fee of $400,000. Aearo can discontinue payment of the fee at any time, in which case it will assume the responsibility for and indemnify Cabot against those liabilities which Cabot’s subsidiary had agreed to retain. The Company anticipates that it will continue to receive payment of the $400,000 fee from Aearo and thereby retain these liabilities for the foreseeable future. Cabot has no liability in connection with any products manufactured by Aearo after 1995.

In addition to Cabot’s subsidiary and as described above, other parties are responsible for significant portions of the costs of respirator liabilities, leaving Cabot’s subsidiary with a portion of the liability in only some of the pending cases. These parties include Aearo, AO, AO’s insurers, another former owner and its insurers and a third-party manufacturer of respirators formerly sold under the AO brand and its insurers (collectively, with the Company’s subsidiary, the “Payor Group”).

As of both September 30, 2019 and 2018, there were approximately 35,000 claimants in pending cases asserting claims against AO in connection with respiratory products. The vast majority of these claims have been pending for more than 10 years with little or no activity and have therefore been excluded from the Company’s estimates of its liability for respirator claims. Cabot has contributed to the Payor Group’s defense and settlement costs with respect to a percentage of pending claims depending on several factors, including the period of alleged product use. In order to quantify Cabot’s estimated share of liability for pending and future respirator liability claims, Cabot has engaged, through counsel, the assistance of Nathan Associates, Inc. (“Nathan”), a leading consulting firm in the field of tort liability valuation. The methodology used to estimate the liability addresses the complexities surrounding Cabot’s potential liability by making assumptions about Cabot’s likely exposure related to claims pending for less than 10 years and the estimated number of future claimants with respect to periods of asbestos, silica and coal mine dust exposure and respirator use. Using those and other assumptions, the Company estimates the costs that would be incurred in defending and resolving both currently pending and future claims. During the year ended September 30, 2019, the Company updated this estimate with the assistance of Nathan. Based on the updated estimate, the Company increased its reserve as of September 30, 2019 for Cabot’s estimated share of the liability for pending and future respirator claims and recorded a charge of $20 million, which is included in Selling and administrative expenses in the Consolidated Statements of Operations. This increase, as well as the higher payments the Company made in fiscal 2019, reflect higher costs of defending and resolving these claims. Based on these estimates, as of September 30, 2019 and 2018, the Company had $35 million and $25 million, respectively, reserved for its estimated share of liability for pending and future respirator claims. In fiscal 2018, the company recorded a charge of $10 million related to the respirator liability which was included in Selling and administrative expenses in the Consolidated Statements of Operations. No charge related to the respirator liability was recorded in fiscal 2017. The Company made payments related to its respirator liability of $10 million in fiscal 2019 and $3 million in both fiscal 2018 and 2017.

The Company’s current estimate of the cost of its share of existing and future respirator liability claims is based on facts and circumstances existing at this time. Developments that could affect the Company’s estimate include, but are not limited to, (i) significant changes in the number of future claims, (ii) changes in the rate of dismissals without payment of pending claims, (iii) significant changes in the average cost of resolving claims, including potential settlements of groups of claims, (iv) significant changes in the legal costs of defending these claims, (v) changes in the nature of claims received, (vi) trial and appellate outcomes, (vii) changes in the law and procedure applicable to these claims, (viii) the financial viability of members of the Payor Group, (ix) a change in the availability of the insurance coverage of the members of the Payor Group or the indemnity provided by AO’s former owner, (x) changes in the allocation of costs among the Payor Group and (xi) a determination that the assumptions that were used to estimate the Company’s share of liability are no longer reasonable. The Company cannot determine the impact of these potential developments on its current estimate of its share of liability for existing and future claims. Accordingly, the actual amount of these liabilities for existing and future claims could be different than the reserved amount.

Other Matters

The Company has various other lawsuits, claims and contingent liabilities arising in the ordinary course of its business and with respect to its divested businesses. The Company does not believe that any of these matters will have a material adverse effect on its financial position; however, litigation is inherently unpredictable. Cabot could incur judgments, enter into settlements or revise its expectations regarding the outcome of certain matters, and such developments could have a material impact on its results of operations in the period in which the amounts are accrued or its cash flows in the period in which the amounts are paid.

Financial Information by Segment & Geographic Area

12 Months Ended

Sep. 30, 2019

Segment Reporting [Abstract]

Financial Information by Segment & Geographic Area

Note U. Financial Information by Segment & Geographic Area

Segment Information

The Company identifies a business as an operating segment if: i) it engages in business activities from which it may earn revenues and incur expenses; ii) its operating results are regularly reviewed by the Chief Operating Decision Maker (“CODM”), who is Cabot’s President and Chief Executive Officer, to make decisions about resources to be allocated to the segment and assess its performance; and iii) it has available discrete financial information. The Company has determined that all of its businesses are operating segments. The CODM reviews financial information at the operating segment level to allocate resources and to assess the operating results and financial performance for each operating segment. Operating segments are aggregated into a reportable segment if the operating segments are determined to have similar economic characteristics and if the operating segments are similar in the following areas: i) nature of products and services; ii) nature of production processes; iii) type or class of customer for their products and services; iv) methods used to distribute the products or provide services; and v) if applicable, the nature of the regulatory environment.

The Company had four reportable segments through June 28, 2019: Reinforcement Materials, Performance Chemicals, Purification Solutions, and Specialty Fluids. The Specialty Fluids business was divested as of June 28, 2019 and since that time Cabot has been organized into the three remaining reportable business segments.

The Reinforcement Materials segment combines the rubber blacks and elastomer composites product lines.

The Performance Chemicals segment combines the specialty carbons, fumed metal oxides and aerogel product lines into the Performance Additives business, and combines the specialty compounds and inkjet colorants product lines into the Formulated Solutions business. These businesses are similar in terms of economic characteristics, nature of products, processes, customer class and product distribution methods, and therefore have been aggregated into one reportable segment.

The Purification Solutions segment represents the Company’s activated carbon business and the Specialty Fluids segment included cesium formate oil and gas drilling fluids and high-purity fine cesium chemicals product lines.

Income (loss) from continuing operations before income taxes (“Segment EBIT”) is presented for each reportable segment in the financial information by the reportable segment table below on the line entitled Income (loss) from continuing operations before taxes. Segment EBIT excludes certain items, meaning items management does not consider representative of on-going operating segment results. In addition, Segment EBIT includes Equity in earnings of affiliated companies, net of tax, the full operating results of a contractual joint venture in Purification Solutions, royalties, Net income (loss) attributable to noncontrolling interests, net of tax, and discounting charges for certain Notes receivable, but excludes Interest expense, foreign currency transaction gains and losses, interest income, dividend income, unearned revenue, general unallocated expense and unallocated corporate costs. Segment assets exclude cash, short-term investments, cost investments, income taxes receivable, deferred taxes and headquarters’ assets, which are included in unallocated and other. Expenditures for additions to long-lived assets include total equity and other investments (including available-for-sale securities) and property, plant and equipment.

Reinforcement Materials

Carbon black is a form of elemental carbon that is manufactured in a highly controlled process to produce particles and aggregates of varied structure and surface chemistry, resulting in many different performance characteristics for a wide variety of applications. Rubber grade carbon blacks are used to enhance the physical properties of the systems and applications in which they are incorporated.

The Company’s rubber blacks products are used in tires and industrial products. Rubber blacks have traditionally been used in the tire industry as a rubber reinforcing agent to increase tread durability and are also used as a performance additive to reduce rolling resistance and improve traction. In industrial products such as hoses, belts, extruded profiles and molded goods, rubber blacks are used to improve the physical performance of the product, including the product’s physical strength, fluid resistance, conductivity and resistivity.

In addition to its rubber blacks products, the Company manufactures compounds of carbon black and rubber using its patented elastomer composites manufacturing process. These compounds improve abrasion/wear resistance, reduce fatigue of rubber parts and reduce rolling resistance compared to carbon black/rubber compounds made by conventional dry mix methods.

Performance Chemicals

Performance Chemicals is organized into two businesses: the Company’s Performance Additives business and its Formulated Solutions business. The Company’s Performance Additives business combines its specialty grades of carbon black, fumed metal oxides and aerogel product lines, and its Formulated Solutions business combines its specialty compounds and inkjet product lines. In Performance Chemicals, the Company designs, manufactures and sells materials that deliver performance in a broad range of customer applications across the automotive, construction, infrastructure, energy, inkjet printing, electronics, and consumer products sectors. The net sales from each of these businesses for fiscal 2019, 2018 and 2017 are as follows:

	Years Ended September 30
	2019		2018		2017
	(In millions)
Performance Additives	$	694	$	707	$	650
Formulated Solutions		301		321		258
Total Performance Chemicals	$	995	$	1,028	$	908

Performance Additives Business

The Company’s specialty grades of carbon black are used to impart color, provide rheology control, enhance conductivity and static charge control, provide UV protection, enhance mechanical properties, and provide formulation flexibility through surface treatment. These specialty carbon products are used in a wide variety of applications, such as inks, coatings, cables, plastics, adhesives, toners, batteries and displays.

Fumed silica is an ultra-fine, high-purity particle used as a reinforcing, thickening, abrasive, thixotropic, suspending or anti-caking agent in a wide variety of products for the automotive, construction, microelectronics, batteries, and consumer products industries. These products include adhesives, sealants, cosmetics, batteries, inks, toners, silicone elastomers, coatings, polishing slurries and pharmaceuticals. Fumed alumina, also an ultra-fine, high-purity particle, is used as an abrasive, absorbent or barrier agent in a variety of products, such as inkjet media, lighting, coatings, cosmetics and polishing slurries.

Aerogel is a hydrophobic, silica-based particle with a high surface area that is used in a variety of thermal insulation and specialty chemical applications. In the building and construction industry, the product is used in insulative sprayable plasters and composite building products, as well as translucent skylight, window, wall and roof systems for insulating eco-daylighting applications. In the specialty chemicals industry, the product is used to provide matte finishing, insulating and thickening properties for use in a variety of applications.

Formulated Solutions Business

Cabot’s masterbatch and conductive compound products, which Cabot refers to as “specialty compounds”, are formulations derived from specialty grades of carbon black mixed with polymers and other additives. These products are generally used by plastic resin producers and converters in applications for the automotive, industrial, packaging, infrastructure, agricultural, consumer products, and electronics industries. As an alternative to directly mixing specialty carbon blacks, these formulations offer greater ease of handling and help customers achieve their desired levels of dispersion and color and manage the addition of small doses of additives. In addition, Cabot’s electrically conductive compound products generally are used to help ensure uniform conductive performance and reduce risks associated with electrostatic discharge in plastics applications.

The Company’s inkjet colorants are high-quality pigment-based black and color dispersions based on its patented carbon black surface modification technology. The dispersions are used in aqueous inkjet inks to impart color, sharp print characteristics and durability, while maintaining high printhead reliability. These products are used in various inkjet printing applications, including commercial printing, small office/home office and corporate office, that require a high level of dispersibility and colloidal stability. Cabot’s inkjet inks, which utilize its pigment-based colorant dispersions, are used in the commercial printing segment for digital print.

Purification Solutions

The Company’s activated carbon products are used for the purification of water, air, food and beverages, pharmaceuticals and other liquids and gases, as either a colorant or a decolorizing agent in the production of products for food and beverage applications and as a chemical carrier in slow release applications. In gas and air applications, one of the uses of activated carbon is for the removal of mercury in flue gas streams. In certain applications, used activated carbon can be reactivated for further use by removing the contaminants from the pores of the activated carbon product. The most common applications for the Company’s reactivated carbon are water treatment and food and beverage purification. In addition to activated carbon production and reactivation, the Company also provides activated carbon solutions through on-site equipment and services, including delivery systems for activated carbon injection in coal-fired utilities, mobile water filter units and carbon reactivation services.

Specialty Fluids

Cabot divested its Specialty Fluids business on June 28, 2019. Refer to Note D for the terms of this transaction. The Specialty Fluids segment produced and marketed a range of cesium products that included cesium formate brines and other fine cesium chemicals. Cesium formate brines are used as a drilling and completion fluid primarily in high pressure and high temperature oil and gas well construction. Fine cesium chemicals are used across a wide range of industries and applications that include catalysts, doping agents and brazing fluxes.

Financial information by reportable segment is as follows:

Years Ended September 30	Reinforcement Materials			Performance Chemicals		Purification Solutions			Specialty Fluids		Segment Total⁽¹⁾		Unallocated and Other^(2), ⁽⁴⁾			Consolidated Total
	(In millions)
2019
Revenues from external customers⁽³⁾	$	1,815		$	995	$	278		$	56	$	3,144	$	193		$	3,337
Depreciation and amortization	$	69		$	51	$	26		$	1	$	147	$	1		$	148
Equity in earnings of affiliated companies	$	(1	)	$	1	$	3		$	—	$	3	$	(2	)	$	1
Income (loss) from continuing operations before income taxes⁽⁴⁾	$	266		$	152	$	2		$	24	$	444	$	(189	)	$	255
Assets⁽⁵⁾	$	1,177		$	1,024	$	436		$	—	$	2,637	$	367		$	3,004
Total expenditures for additions to long-lived assets⁽⁶⁾	$	82		$	148	$	11		$	1	$	242	$	5		$	247
2018
Revenues from external customers⁽³⁾	$	1,774		$	1,028	$	279		$	45	$	3,126	$	116		$	3,242
Depreciation and amortization	$	70		$	48	$	32		$	2	$	152	$	(3	)	$	149
Equity in earnings of affiliated companies	$	1		$	—	$	6		$	—	$	7	$	(5	)	$	2
Income (loss) from continuing operations before income taxes⁽⁴⁾	$	279		$	200	$	(7	)	$	8	$	480	$	(363	)	$	117
Assets⁽⁵⁾	$	1,319		$	919	$	460		$	178	$	2,876	$	368		$	3,244
Total expenditures for additions to long-lived assets⁽⁶⁾	$	97		$	94	$	16		$	17	$	224	$	5		$	229
2017
Revenues from external customers⁽³⁾	$	1,381		$	908	$	281		$	41	$	2,611	$	106		$	2,717
Depreciation and amortization	$	69		$	46	$	39		$	2	$	156	$	(1	)	$	155
Equity in earnings of affiliated companies	$	6		$	—	$	6		$	—	$	12	$	(5	)	$	7
Income (loss) from continuing operations before income taxes⁽⁴⁾	$	193		$	201	$	6		$	9	$	409	$	(110	)	$	299
Assets⁽⁵⁾	$	1,189		$	708	$	741		$	140	$	2,778	$	560		$	3,338
Total expenditures for additions to long-lived assets⁽⁶⁾	$	68		$	47	$	19		$	5	$	139	$	8		$	147

⁽¹⁾	Cabot divested its Specialty Fluids business on June 28, 2019. Refer to Note D for the terms of this transaction.

⁽²⁾	Unallocated and Other includes certain items and eliminations necessary to reflect management’s reporting of operating segment results. These items are reflective of the segment reporting presented to the CODM.

⁽³⁾

Consolidated Total Revenues from external customers reconciles to Net sales and other operating revenues on the Consolidated Statements of Operations. Revenues from external customers that are categorized as Unallocated and Other reflects royalties, external shipping and handling fees, the impact of unearned revenue, the removal of 100% of the sales of an equity method affiliate and discounting charges for certain Notes receivable. Details are provided in the table below.

	Years Ended September 30
	2019			2018		2017
	(In millions)
Royalties, the impact of unearned revenue, the removal of 100% of the sales of an equity method affiliate and discounting charges for certain Notes receivable	$	(13	)	$	11	$	11
Shipping and handling fees		130			105		95
By-product sales^(a)		76			—		—
Total	$	193		$	116	$	106

^(a)

^{As of October 1, 2018, as part of the adoption of the new FASB accounting standard, Revenue from Contracts with Customers, the Company began presenting revenue from by-products produced in manufacturing operations in Net sales and other operating revenues, which in prior years was included as a reduction in Cost of sales.}

⁽⁴⁾

Consolidated Total Income (loss) from continuing operations before income taxes reconciles to Income (loss) from continuing operations before income taxes and equity in earnings of affiliated companies on the Consolidated Statements of Operations. Total Income (loss) from continuing operations before income taxes that are categorized as Unallocated and Other includes:

	Years Ended September 30
	2019			2018			2017
	(In millions)
Interest expense	$	(59	)	$	(54	)	$	(53	)
Certain items:^(a)
Specialty Fluids loss on sale and asset impairment charge (Note D)		(29	)		—			—
Legal and environmental matters and reserves		(21	)		(16	)		1
Global restructuring activities (Note P)		(16	)		30			(3	)
Equity affiliate investment impairment charge (Note M)		(11	)		—			—
Acquisition and integration-related charges		(6	)		(2	)		—
Executive transition costs		(1	)		(2	)		—
Purification Solutions goodwill and long-lived assets impairment charge (Note G)		—			(254	)		—
Inventory reserve adjustment		—			(13	)		—
Gains (losses) on sale of investments		—			10			—
Other certain items		(3	)		(1	)		(1	)
Total certain items, pre-tax		(87	)		(248	)		(3	)
Unallocated corporate costs^(b)		(50	)		(61	)		(50	)
General unallocated income (expense)^(c)		8			2			3
Less: Equity in earnings of affiliated companies, net of tax^(d)		1			2			7
Total	$	(189	)	$	(363	)	$	(110	)

^(a)

Certain items are items that management does not consider representative of operating segment results and they are, therefore, excluded from Segment EBIT.

^(b)

Unallocated corporate costs are not controlled by the segments and primarily benefit corporate interests.

^(c)

General unallocated income (expense) consists of gains (losses) arising from foreign currency transactions, net of other foreign currency risk management activities, interest income, dividend income, the profit or loss related to the corporate adjustment for unearned revenue, and the impact of including the full operating results of a contractual joint venture in Purification Solutions Segment EBIT.

^(d)

Equity in earnings of affiliated companies, net of tax is included in Segment EBIT and is removed from Unallocated and other to reconcile to income (loss) from operations before taxes.

⁽⁵⁾	Unallocated and Other assets includes cash, marketable securities, cost investments, income taxes receivable, deferred taxes, headquarters’ assets, and current and non-current assets held for sale.

⁽⁶⁾	Expenditures for additions to long-lived assets include total equity and other investments (including available-for-sale securities) and property, plant and equipment.

Geographic Information

Revenues from external customers attributable to an individual country, other than the U.S. and China, were not material for disclosure. Revenues from external customers by individual country are summarized as follows:

	Years Ended September 30
	2019		2018		2017
	(In millions)
United States	$	702	$	676	$	645
China		738		752		573
Other countries		1,897		1,814		1,499
Total	$	3,337	$	3,242	$	2,717

Each of the Company’s segments operate globally. In addition to presenting Revenue from external customers by reportable segment, the following tables further disaggregate Revenue from external customers by geographic region.

	Year Ended September 30, 2019
	Reinforcement Materials		Performance Chemicals		Purification Solutions		Specialty Fluids		Consolidated Total
	(In millions)
Americas	$	688	$	294	$	126	$	6	$	1,114
Asia Pacific		769		353		35		1		1,158
Europe, Middle East and Africa		358		348		117		49		872
Segment revenues from external customers		1,815		995		278		56		3,144
Unallocated and other										193
Net sales and other operating revenues									$	3,337

Long-lived assets attributable to an individual country, other than the U.S. and China, were not material for disclosure. Long-lived asset information by individual country is summarized as follows:

	Years Ended September 30
	2019		2018		2017
	(In millions)
United States	$	572	$	493	$	493
China		264		270		261
Other countries		512		533		551
Total	$	1,348	$	1,296	$	1,305

Unaudited Quarterly Financial Information

12 Months Ended

Sep. 30, 2019

Quarterly Financial Information Disclosure [Abstract]

Unaudited Quarterly Financial Information

Note V. Unaudited Quarterly Financial Information

Unaudited financial results by quarter for fiscal 2019 and 2018 are summarized below:

	Quarters Ended								Year Ended
	December 31,		March 31,		June 30,		September 30,		September 30,
	2018		2019		2019		2019		2019
	(In millions, except per share amounts)
Net sales and other operating revenues	$	821	$	844	$	845	$	827	$	3,337
Gross profit	$	166	$	178	$	170	$	171	$	685
Net income (loss)	$	77	$	29	$	40	$	40	$	186
Net income (loss) attributable to Cabot Corporation	$	69	$	23	$	32	$	33	$	157
Earnings per common share—basic	$	1.14	$	0.39	$	0.55	$	0.56	$	2.64
Earnings per common share—diluted	$	1.14	$	0.39	$	0.55	$	0.55	$	2.63

During the fourth quarter of fiscal 2019, Cabot recorded a pre-tax charge of $20 million related to its respirator liabilities as discussed further in Note T.

	Quarters Ended										Year Ended
	December 31,			March 31,			June 30,		September 30,		September 30,
	2017			2018			2018		2018		2018
	(In millions, except per share amounts)
Net sales and other operating revenues	$	720		$	818		$	854	$	850	$	3,242
Gross profit	$	176		$	188		$	197	$	211	$	772
Net income (loss)	$	(112	)	$	(163	)	$	99	$	102	$	(74	)
Net income (loss) attributable to Cabot Corporation	$	(122	)	$	(173	)	$	88	$	94	$	(113	)
Earnings per common share—basic	$	(1.98	)	$	(2.80	)	$	1.41	$	1.51	$	(1.85	)
Earnings per common share—diluted	$	(1.98	)	$	(2.80	)	$	1.40	$	1.51	$	(1.85	)

During the fourth quarter of fiscal 2018, Cabot recorded a pre-tax gain of $28 million on the sale of its land rights in Thane, India as discussed further in Note P. In addition, the tax benefit for the fourth quarter of fiscal 2018 includes a $19 million net benefit from discrete tax items primarily related to a revision of the estimate of the impact of the recent U.S. tax reform as discussed further in Note S.

Significant Accounting Policies (Policies)

12 Months Ended

Sep. 30, 2019

Accounting Policies [Abstract]

Principles of Consolidation

Cash and Cash Equivalents

Inventories

Investments

Intangible Assets and Goodwill Impairment

Long-Lived Assets Impairment

Long-lived Assets Impairment

Property, Plant and Equipment

Asset Retirement Obligations

Foreign Currency Translation

Share Repurchase

Share Repurchases

Financial Instruments

Revenue Recognition

The Company does not have contract assets or liabilities that are material.

Cost of Sales

Accounts and Notes Receivable

Stock-Based Compensation

Stock-based Compensation

Selling and Administrative Expenses

Selling and administrative expenses consist of salaries and fringe benefits of sales and office personnel, general office expenses and other expenses not directly related to manufacturing operations.

Research and Technical Expenses

Research and technical expenses include salaries, equipment and material expenditures, and contractor fees and are expensed as incurred.

Income Taxes

Environmental Costs

Use of Estimates

Recently Adopted Accounting Standards

Consolidated Statements of Operations	Years Ended September 30
	2018							2017
	As Originally Reported		Effect of Change			As Adjusted		As Originally Reported			Effect of Change			As Adjusted

Cost of sales	$	2,461	$	9		$	2,470	$	2,054		$	6		$	2,060
Gross profit	$	781	$	(9	)	$	772	$	663		$	(6	)	$	657
Selling and administrative expenses	$	305	$	3		$	308	$	260		$	2		$	262
Research and technical expenses	$	66	$	—		$	66	$	56		$	1		$	57
Income (loss) from operations	$	156	$	(12	)	$	144	$	347		$	(9	)	$	338
Other income (expense)	$	5	$	12		$	17	$	(4	)	$	9		$	5

Recently Issued Accounting Pronouncements

Recent Accounting Pronouncements (Tables)

12 Months Ended

Sep. 30, 2019

Accounting Policies [Abstract]

Schedule of Change Retrospectively to Prior Periods Financial Statement Line Items

The Company adopted the standard on October 1, 2018 and used a retrospective transition method to reclassify net periodic benefit cost, other than the service component, from Cost of sales, Selling and administrative expenses and Research and technical expenses to Other income (expense) in the Consolidated Statements of Operations for the prior periods presented. In accordance with the standard, the Company utilized prior period footnote disclosures as a practical expedient to apply these retrospective presentations, which is shown in the table below:

Consolidated Statements of Operations	Years Ended September 30
	2018							2017
	As Originally Reported		Effect of Change			As Adjusted		As Originally Reported			Effect of Change			As Adjusted

Cost of sales	$	2,461	$	9		$	2,470	$	2,054		$	6		$	2,060
Gross profit	$	781	$	(9	)	$	772	$	663		$	(6	)	$	657
Selling and administrative expenses	$	305	$	3		$	308	$	260		$	2		$	262
Research and technical expenses	$	66	$	—		$	66	$	56		$	1		$	57
Income (loss) from operations	$	156	$	(12	)	$	144	$	347		$	(9	)	$	338
Other income (expense)	$	5	$	12		$	17	$	(4	)	$	9		$	5

Inventories (Tables)

12 Months Ended

Sep. 30, 2019

Inventory Disclosure [Abstract]

Components of Company's Inventories

Inventories, net of obsolete, unmarketable and slow moving reserves, are as follows:

	September 30
	2019		2018
	(In millions)
Raw materials	$	107	$	129
Work in process		—		3
Finished goods		305		329
Other		54		50
Total	$	466	$	511

Property, Plant and Equipment (Tables)

12 Months Ended

Sep. 30, 2019

Property Plant And Equipment [Abstract]

Components of Property, Plant and Equipment

Property, plant and equipment consists of the following:

	September 30
	2019			2018
	(In millions)
Land and land improvements	$	144		$	142
Buildings		524			514
Machinery and equipment		2,369			2,373
Other		247			249
Construction in progress		262			242
Total property, plant and equipment		3,546			3,520
Less: Accumulated depreciation		(2,198	)		(2,224	)
Net property, plant and equipment	$	1,348		$	1,296

Purification Solutions Goodwill and Long-Lived Assets Impairment Charges (Tables)

12 Months Ended

Sep. 30, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

Impairment Charges and Associated Deferred Tax Benefit

	Three Months Ended March 31, 2018
	(In millions)
Purification Solutions goodwill impairment charge	$	92
Purification Solutions long-lived assets impairment charge		162
Benefit for income taxes		(30	)
Impairment charges, after tax	$	224

Goodwill and Intangible Assets (Tables)

12 Months Ended

Sep. 30, 2019

Goodwill And Intangible Assets Disclosure [Abstract]

Schedule of Goodwill Balances

The carrying amount of goodwill attributable to each reportable segment with goodwill balances and the changes in those balances during the period ended September 30, 2019 are as follows

	Reinforcement Materials			Performance Chemicals			Purification Solutions ⁽¹⁾		Total
	(In millions)
Balance at September 30, 2018	$	52		$	41		$	—	$	93
Foreign currency impact		(2	)		(1	)		—		(3	)
Balance at September 30, 2019	$	50		$	40		$	—	$	90

⁽¹⁾

Schedule of Intangible Assets

The following table provides information regarding the Company’s intangible assets:

	September 30, 2019							September 30, 2018
	Gross Carrying Value		Accumulated Amortization			Net Intangible Assets		Gross Carrying Value		Accumulated Amortization			Net Intangible Assets
	(In millions)
Intangible assets with finite lives
Developed technologies	$	50	$	(5	)	$	45	$	52	$	(2	)	$	50
Trademarks		8		—			8		8		—			8
Customer relationships		57		(14	)		43		51		(11	)		40
Total intangible assets	$	115	$	(19	)	$	96	$	111	$	(13	)	$	98

Accounts Payable, Accrued Liabilities and Other Liabilities (Tables)

12 Months Ended

Sep. 30, 2019

Payables And Accruals [Abstract]

Components of Accounts Payable and Accrued Liabilities

Accounts payable and accrued liabilities included in current liabilities consist of the following:

	September 30
	2019		2018
	(In millions)
Accounts payable	$	390	$	446
Accrued employee compensation		51		70
Other accrued liabilities		96		97
Total	$	537	$	613

Components of Other Long-Term Liabilities

Other long-term liabilities consist of the following:

	September 30
	2019		2018
	(In millions)
Employee benefit plan liabilities	$	91	$	118
Non-current tax liabilities		12		19
Other accrued liabilities		103		115
Total	$	206	$	252

Debt and Other Obligations (Tables)

12 Months Ended

Sep. 30, 2019

Debt Disclosure [Abstract]

Schedule of Long-Term Obligations

The Company’s long-term obligations, the fiscal year in which they mature and their respective interest rates are summarized below:

	September 30
	2019			2018
	(In millions)
Variable Rate Debt:
Revolving Credit Facility, expires fiscal 2023	$	—		$	—
Revolving Credit Facility - Canada, expires fiscal 2021		43			90
Revolving Credit Facility - Euro, expires fiscal 2024		56			—
Total variable rate debt		99			90
Fixed Rate Debt:
3.7% Notes due fiscal 2022		350			350
3.4% Notes due fiscal 2026		250			250
4.0% Notes due fiscal 2029		300			—
Medium Term Notes:
Notes matured fiscal 2019, 7.42%		—			30
Notes due fiscal 2022, 8.34% — 8.47%		15			15
Notes due fiscal 2028, 6.57% — 7.28%		8			8
Total Medium Term Notes		23			53
Chinese Renminbi Debt, matured fiscal 2019, 4.35%		—			4
Chinese Renminbi Debt, due fiscal 2020, 4.35%		4			—
Total fixed rate debt		927			657
Capital lease obligations, due through fiscal 2033		12			11
Unamortized debt issuance costs and debt discount		(7	)		(4	)
Total debt		1,031			754
Less current portion of long-term debt		(7	)		(35	)
Total long-term debt	$	1,024		$	719

Schedule of Future Years Payment

The aggregate principal amounts of long-term debt and capital lease obligations due in each of the five years from fiscal 2020 through 2024 and thereafter are as follows:

Years Ending September 30	Principal Payments on Long-Term Debt		Payments on Capital Lease Obligations			Total
	(In millions)
2020	$	4	$	3		$	7
2021		43		3			46
2022		365		3			368
2023		—		3			3
2024		56		2			58
Thereafter		558		7			565
Less: Interest		—		(9	)		(9	)
Total	$	1,026	$	12		$	1,038

Derivatives (Tables)

12 Months Ended

Sep. 30, 2019

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Details of Derivatives Held to Manage Foreign Currency Risk

The following table provides details of the derivatives held as of September 30, 2019 and 2018 to manage foreign currency risk.

		Notional Amount
Description	Borrowing	September 30, 2019	September 30, 2018	Hedge Designation
Cross Currency Swaps	3.4% Notes	USD 250 million swapped to EUR 223 million	USD 250 million swapped to EUR 223 million	Net investment
Forward Foreign Currency Contracts⁽¹⁾	N/A	USD 54 million	USD 18 million	No designation

⁽¹⁾	Cabot’s forward foreign exchange contracts are denominated in British pound, Canadian dollar, Indonesian rupiah and Czech koruna.

Summary Impact of Cross-currency Swaps to AOCI and Consolidated Statements of Operations

The following table summarizes the impact of the cross-currency swaps to AOCI and the Consolidated Statements of Operations:

	Years Ended September 30
	2019		2018			2017			2019			2018			2017		2019		2018		2017
Description	Gain/(Loss) Recognized in AOCI								(Gain)/Loss Reclassified from AOCI into Interest Expense in the Consolidated Statements of Operations								(Gain)/Loss Recognized in Interest Expense in the Consolidated Statements of Operations (Amount Excluded from Effectiveness Testing)
	(In millions)
Cross-currency swaps	$	23	$	(2	)	$	(10	)	$	(5	)	$	(5	)	$	—	$	1	$	2	$	—

- Definition

Tabular disclosure of pertinent information about a derivative or group of derivatives on a disaggregated basis, such as for individual instruments, or small groups of similar instruments. May include a combination of the type of instrument, risks being hedged, notional amount, hedge designation, related hedged item, inception date, maturity date, or other relevant item.

+ References

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+ Details

Employee Benefit Plans (Tables)

12 Months Ended

Sep. 30, 2019

Compensation And Retirement Disclosure [Abstract]

Change in Benefit Obligations and Change in Plan Assets

	Years Ended September 30
	2019						2018						2019						2018
	Pension Benefits												Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign			U.S.			Foreign
	(In millions)
Change in Benefit Obligations:
Benefit obligation at beginning of year	$	143		$	373		$	160		$	376		$	29		$	19		$	33		$	20
Service cost		1			7			1			9			—			—			—			—
Interest cost		5			5			5			7			1			1			1			1
Plan participants’ contribution		—			1			—			2			—			—			—			—
Foreign currency exchange rate changes		—			(13	)		—			(7	)		—			(1	)		—			(1	)
(Gain) Loss from changes in actuarial assumptions and plan experience		21			—			(10	)		2			1			2			(2	)		—
Benefits paid		(11	)		(7	)		(7	)		(13	)		(3	)		(1	)		(3	)		(1	)
Settlements or curtailments		(1	)		(134	)		(5	)		(2	)		—			—			—			—
Divestiture of Specialty Fluids		—			(13	)		—			—			—			—			—			—
Other		(1	)		1			(1	)		(1	)		—			—			—			—
Benefit obligation at end of year	$	157		$	220		$	143		$	373		$	28		$	20		$	29		$	19

	Years Ended September 30
	2019						2018						2019						2018
	Pension Benefits												Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign			U.S.			Foreign
	(In millions)
Change in Plan Assets:
Fair value of plan assets at beginning of year	$	149		$	323		$	156		$	318		$	—		$	—		$	—		$	—
Actual return on plan assets		14			17			4			17			—			—			—			—
Employer contribution		1			7			1			9			3			1			3			1
Plan participants’ contribution		—			1			—			2			—			—			—			—
Foreign currency exchange rate changes		—			(11	)		—			(7	)		—			—			—			—
Benefits paid		(11	)		(7	)		(7	)		(13	)		(3	)		(1	)		(3	)		(1	)
Settlements		(1	)		(124	)		(4	)		(2	)		—			—			—			—
Divestiture		—			(10	)		—			—			—			—			—			—
Expenses paid from assets		(1	)		(1	)		(1	)		(1	)		—			—			—			—
Fair value of plan assets at end of year	$	151		$	195		$	149		$	323		$	—		$	—		$	—		$	—
Funded status	$	(6	)	$	(25	)	$	6		$	(50	)	$	(28	)	$	(20	)	$	(29	)	$	(19	)
Recognized asset (liability)	$	(6	)	$	(25	)	$	6		$	(50	)	$	(28	)	$	(20	)	$	(29	)	$	(19	)

Assumptions Used to Determine Pension Benefit Obligations and Periodic Benefit Costs, Postretirement Benefit Obligations and Net Costs

Pension Assumptions and Strategy

The following assumptions were used to determine the pension benefit obligations and periodic benefit costs as of and for the years ended September 30:

	2019						2018						2017
	Pension Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign
Actuarial assumptions as of the year-end measurement date:
Discount rate		2.6	%		1.8	%		4.2	%		2.4	%		3.6	%		2.4	%
Rate of increase in compensation	N/A				3.0	%	N/A				2.7	%	N/A				2.7	%
Actuarial assumptions used to determine net periodic benefit cost during the year:
Discount rate - benefit obligation		4.2	%		2.4	%		3.6	%		2.4	%		3.4	%		1.8	%
Discount rate - service cost	N/A				2.5	%	N/A				2.4	%	N/A				1.8	%
Discount rate - interest cost		3.9	%		2.1	%		3.0	%		2.0	%		2.7	%		1.5	%
Expected long-term rate of return on plan assets		6.3	%		4.9	%		6.8	%		4.9	%		6.8	%		4.7	%
Rate of increase in compensation	N/A				2.7	%	N/A				2.7	%	N/A				2.8	%

Postretirement Assumptions and Strategy

The following assumptions were used to determine the postretirement benefit obligations and net costs as of and for the years ended September 30:

	2019						2018						2017
	Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign
Actuarial assumptions as of the year-end measurement date:
Discount rate		2.9	%		2.4	%		4.1	%		3.2	%		3.4	%		3.1	%
Initial health care cost trend rate		6.5	%		6.9	%		7.0	%		7.0	%		7.0	%		7.1	%
Actuarial assumptions used to determine net cost during the year:
Discount rate - benefit obligation		4.1	%		3.2	%		3.4	%		3.1	%		3.0	%		2.8	%
Discount rate - service cost		4.0	%		3.5	%		3.1	%		3.6	%		2.6	%		3.2	%
Discount rate - interest cost		3.7	%		3.1	%		2.8	%		3.0	%		2.4	%		2.6	%
Initial health care cost trend rate		7.0	%		7.0	%		7.0	%		7.1	%		7.0	%		6.1	%

Amounts Recognized in Consolidated Balance Sheets

Amounts recognized in the Consolidated Balance Sheets at September 30, 2019 and 2018 related to the Company's defined benefit pension and postretirement benefit plans were as follows:

	September 30
	2019						2018						2019						2018
	Pension Benefits												Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign			U.S.			Foreign
	(In millions)
Noncurrent assets	$	—		$	19		$	10		$	21		$	—		$	—		$	—		$	—
Current liabilities	$	(3	)	$	(1	)	$	—		$	(1	)	$	(3	)	$	—		$	(3	)	$	(1	)
Noncurrent liabilities	$	(3	)	$	(43	)	$	(4	)	$	(70	)	$	(25	)	$	(20	)	$	(26	)	$	(18	)

Amounts Recognized in AOCI

Amounts recognized in AOCI at September 30, 2019 and 2018 related to the Company's defined benefit pension and postretirement benefit plans were as follows:

	September 30
	2019				2018						2019					2018
	Pension Benefits										Postretirement Benefits
	U.S.		Foreign		U.S.			Foreign			U.S.			Foreign		U.S.			Foreign
	(In millions)
Net actuarial (gain) loss	$	13	$	36	$	(1	)	$	49		$	(6	)	$	6	$	(7	)	$	4
Net prior service credit		—		—		—			(1	)		—			—		(2	)		—
Balance in accumulated other comprehensive income (loss), pretax	$	13	$	36	$	(1	)	$	48		$	(6	)	$	6	$	(9	)	$	4

Estimated Future Benefit Payments

The Company expects that the following benefit payments will be made to plan participants in the years from 2020 to 2029:

	Pension Benefits				Postretirement Benefits
Years Ending September 30	U.S.		Foreign		U.S.		Foreign
	(In millions)
2020⁽¹⁾	$	158	$	9	$	3	$	1
2021	$	—	$	12	$	3	$	1
2022	$	—	$	10	$	3	$	1
2023	$	—	$	10	$	3	$	1
2024	$	—	$	11	$	3	$	1
2025 - 2029	$	1	$	55	$	10	$	4

⁽¹⁾	^{The $158 million expected payment for U.S. pension benefits in fiscal 2020 is in connection with the termination of the U.S. plan which is expected to be completed in fiscal 2020.}

Net Periodic Defined Benefit Pension and Other Postretirement Benefit Costs

Net periodic defined benefit pension and other postretirement benefit costs include the following components:

	Years Ended September 30
	2019						2018						2017						2019					2018					2017
	Pension Benefits																		Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign			U.S.			Foreign		U.S.			Foreign		U.S.			Foreign
	(In millions)
Service cost	$	1		$	7		$	1		$	9		$	1		$	10		$	—		$	—	$	—		$	—	$	—		$	—
Interest cost		5			5			5			7			4			6			1			1		1			1		1			1
Expected return on plan assets		(9	)		(10	)		(10	)		(15	)		(9	)		(14	)		—			—		—			—		—			—
Amortization of prior service cost		—			2			—			—			—			—			(2	)		—		(3	)		—		(3	)		—
Net losses		—			2			—			3			—			5			(1	)		—		(1	)		—		—			—
Settlements or Curtailments cost		—			(7	)		—			—			—			—			—			—		—			—		—			—
Net periodic (benefit) cost	$	(3	)	$	(1	)	$	(4	)	$	4		$	(4	)	$	7		$	(2	)	$	1	$	(3	)	$	1	$	(2	)	$	1

Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss), Pre-Tax

Other changes in plan assets and benefit obligations recognized in Other comprehensive income (loss) are as follows:

	Years Ended September 30
	2019					2018						2017						2019				2018						2017
	Pension Benefits																	Postretirement Benefits
	U.S.		Foreign			U.S.			Foreign			U.S.			Foreign			U.S.		Foreign		U.S.			Foreign			U.S.			Foreign
	(In millions)
Net (gains) losses	$	14	$	(16	)	$	(4	)	$	—		$	(9	)	$	(35	)	$	—	$	2	$	(2	)	$	(1	)	$	(3	)	$	(1	)
Prior service (credit) cost		—		3			—			—			—			—			—		—		—			—			—			—
Amortization of prior service credit		—		(2	)		—			—			—			—			2		—		3			—			3			—
Amortization of prior unrecognized loss		—		(2	)		—			(3	)		—			(5	)		1		—		1			—			—			—
Loss on divestiture		—		(2	)		—			—			—			—			—		—		—			—			—			—
Gain on settlements		—		7			—			—			—			—			—		—		—			—			—			—
Other		—		—			—			—			—			—			—		—		—			—			—			—
Net changes recognized in Total other comprehensive (income) loss ⁽¹⁾	$	14	$	(12	)	$	(4	)	$	(3	)	$	(9	)	$	(40	)	$	3	$	2	$	2		$	(1	)	$	—		$	(1	)

⁽¹⁾	^{The tax impact on pension and other postretirement benefit liability adjustments arising during the period was a tax benefit of $5 million, tax provision of $1 million, and tax provision of $7 million for fiscal years 2019, 2018, and 2017, respectively.}

Sensitivity Analysis

Defined Benefit Pension Plans Weighted-Average Asset Allocations

The Company’s defined benefit pension plans weighted-average asset allocations at September 30, 2019 and 2018 by asset category, are as follows:

	September 30
	2019						2018
	Pension Assets
	U.S.			Foreign			U.S.			Foreign
Equity securities		—	%		39	%		40	%		39	%
Debt securities		68	%		50	%		60	%		53	%
Cash and other securities		32	%		11	%		—	%		8	%
Total		100	%		100	%		100	%		100	%

Fair Value of Pension Plan Assets by Asset Category

The fair value of the Company’s pension plan assets at September 30, 2019 and 2018 by asset category is as follows:

	September 30
	2019						2018
	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Observable Inputs (Level 2)		Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Observable Inputs (Level 2)		Total
	(In millions)
Cash	$	2	$	—	$	2	$	3	$	—	$	3
Direct investments:
U.S government bonds		—		—		—		17		13		30
U.S. corporate bonds		—		—		—		—		74		74
Non-U.S. equities		3		—		3		—		—		—
Non-U.S. government bonds		2		—		2		—		—		—
Non-U.S. corporate bonds		3		—		3		—		—		—
Mortgage backed securities		—		1		1		—		—		—
Other fixed income		1		—		1		—		—		—
Total direct investments		9		1		10		17		87		104
Investment funds:
Equity funds⁽¹⁾		—		74		74		44		126		170
Fixed income funds⁽²⁾		104		90		194		—		169		169
Real estate funds⁽³⁾		—		12		12		—		9		9
Cash equivalent funds		48		—		48		1		—		1
Total investment funds		152		176		328		45		304		349
Alternative investments:
Insurance contracts⁽⁴⁾		—		5		5		—		16		16
Other alternative investments		1		—		1		—		—		—
Total alternative investments		1		5		6		—		16		16
Total pension plan assets	$	164	$	182	$	346	$	65	$	407	$	472

⁽¹⁾	The equity funds asset class includes funds that invest in U.S. equities as well as equity securities issued by companies incorporated, listed or domiciled in countries in developed and/or emerging markets. These companies may be in the small-, mid- or large-cap categories.

⁽²⁾

⁽³⁾

⁽⁴⁾	Insurance contracts held by the Company’s non-U.S. plans are issued by well-known, highly rated insurance companies.

Stock-Based Compensation (Tables)

12 Months Ended

Sep. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation Expenses

The following table presents stock-based compensation expenses included in the Company’s Consolidated Statements of Operations:

	Years Ended September 30
	2019			2018			2017
	(In millions)
Cost of sales	$	1		$	2		$	1
Selling and administrative expenses		9			19			14
Research and technical expenses		1			1			1
Stock-based compensation expense		11			22			16
Income tax benefit		(3	)		(6	)		(6	)
Net stock-based compensation expense	$	8		$	16		$	10

Equity Incentive Plan Activity

The following table summarizes the total stock option and restricted stock unit activity in the equity incentive plans for fiscal 2019:

	Stock Options							Restricted Stock Units
	Total Options ⁽⁴⁾			Weighted Average Exercise Price		Weighted Average Grant Date Fair Value		Restricted Stock Units⁽¹⁾			Weighted Average Grant Date Fair Value
	(Shares in thousands)
Outstanding at September 30, 2018		881		$	50.73	$	13.82		985		$	50.16
Granted		343		$	49.70	$	10.85		316		$	49.44
Performance-based adjustment⁽²⁾		—		$	—	$	—		10		$	62.98
Exercised / Vested		(49	)	$	35.06	$	9.41		(383	)	$	40.97
Cancelled / Forfeited		(153	)	$	54.44	$	10.36		(163	)	$	54.48
Outstanding at September 30, 2019⁽³⁾		1,022		$	50.57	$	12.13		765		$	53.71
Exercisable at September 30, 2019		499		$	48.09

⁽¹⁾	The number granted represents the number of shares issuable upon vesting of time-based restricted stock units and performance-based restricted stock units, assuming the Company performs at the target performance level in each year of the three-year performance period.

⁽²⁾	Represents the net incremental number of shares issuable upon vesting of performance-based restricted stock units based upon the achievement of the annual financial performance metrics for fiscal 2019.

⁽³⁾	Stock options outstanding include options vested and expected to vest in the future and have a weighted average remaining contractual life of 6.74 years.

⁽⁴⁾	Unvested stock options were approximately 523,000 and 546,000 at September 30, 2019 and 2018 and their weighted average grant date fair values were $52.95 and $54.48, respectively.

Weighted-Average Assumptions

The fair values on the grant date were calculated using the following weighted-average assumptions:

	Years Ended September 30
	2019			2018			2017
Expected stock price volatility		27	%		28	%		32	%
Risk free interest rate		3.1	%		2.2	%		1.8	%
Expected life of options (years)		6			6			6
Expected annual dividends per year	$	1.32		$	1.26		$	1.20

Restructuring (Tables)

12 Months Ended

Sep. 30, 2019

Restructuring And Related Activities [Abstract]

Recorded Restructuring Activities

Cabot’s restructuring activities were recorded in the Consolidated Statements of Operations as follows:

	Years Ended September 30
	2019		2018			2017
	(In millions)
Cost of sales	$	9	$	(31	)	$	2
Selling and administrative expenses		7		1			1
Total	$	16	$	(30	)	$	3

Restructuring Activities and Related Reserves

Details of all restructuring activities and the related reserves for fiscal 2017, 2018, and 2019 were as follows:

	Severance and Employee Benefits			Environmental Remediation and Decommissioning Activities			Non-Cash Asset Impairment and Accelerated Depreciation			Asset Sales			Other			Total
	(In millions)
Reserve at September 30, 2016	$	3		$	2		$	—		$	—		$	—		$	5
Charges (gain)		1			1			—			—			1			3
Costs charged against assets		—			—			—			—			1			1
Cash (paid) received		(3	)		(1	)		—			—			(2	)		(6	)
Reserve at September 30, 2017		1			2			—			—			—			3
Charges (gain)		2			3			1			(38	)		2			(30	)
Costs charged against liabilities		—			—			(1	)		(1	)		—			(2	)
Cash paid		(2	)		(1	)		—			39			(2	)		34
Reserve at September 30, 2018		1			4			—			—			—			5
Charges (gain)		11			—			2			—			3			16
Costs charged against assets		—			—			(2	)		—			—			(2	)
Cash (paid) received		(9	)		—			—			—			(3	)		(12	)
Reserve at September 30, 2019	$	3		$	4		$	—		$	—		$	—		$	7

Accumulated Other Comprehensive Income (Loss) (Tables)

12 Months Ended

Sep. 30, 2019

Equity [Abstract]

Changes in Each Component of AOCI, Net of Tax

Changes in each component of AOCI, net of tax, are as follows for fiscal 2018 and 2019:

	Currency Translation Adjustment			Unrealized Gains on Investment			Pension and Other Postretirement Benefit Liability Adjustment			Total
	(In millions)
Balance at September 30, 2017 attributable to Cabot Corporation	$	(204	)	$	2		$	(57	)	$	(259	)
Other comprehensive income (loss) before reclassifications		(64	)		(1	)		6			(59	)
Amounts reclassified from AOCI		(2	)		—			(1	)		(3	)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		(4	)		—			—			(4	)
Balance at September 30, 2018 attributable to Cabot Corporation		(266	)		1			(52	)		(317	)
Other comprehensive income (loss) before reclassifications		(69	)		—			4			(65	)
Amounts reclassified from AOCI		(9	)		—			(6	)		(15	)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		(6	)		—			—			(6	)
Balance at September 30, 2019 attributable to Cabot Corporation	$	(338	)	$	1		$	(54	)	$	(391	)

Amounts Reclassified Out of AOCI

The amounts reclassified out of AOCI and into the Consolidated Statements of Operations for the fiscal years ended September 30, 2019, 2018 and 2017 are as follows:

	Affected Line Item in the Consolidated	Years Ended September 30
	Statements of Operations	2019			2018			2017
		(In Millions)
Derivatives: net investment hedges
(Gains) losses reclassified to interest expense	Interest expense	$	(5	)	$	(5	)	$	—
(Gains) losses excluded from effectiveness testing and amortized to interest expense	Interest expense		1			2			—
Pension and other postretirement benefit liability adjustment
Amortization of actuarial losses	Net Periodic Benefit Cost - see Note N for details		1			2			5
Amortization of prior service cost (credit)	Net Periodic Benefit Cost - see Note N for details		—			(3	)		(3	)
Settlement and curtailment gain	Net Periodic Benefit Cost - see Note N for details		(7	)		—			—
Specialty Fluids divestiture	Specialty Fluids loss on sale and asset impairment - see Note D for details		(3	)		—			—
Total before tax			(13	)		(4	)		2
Tax impact	Provision (benefit) for income taxes		(2	)		1			—
Total after tax		$	(15	)	$	(3	)	$	2

Earnings Per Share (Tables)

12 Months Ended

Sep. 30, 2019

Earnings Per Share [Abstract]

Components of Basic and Diluted Earnings Per Common Share (EPS)

The following tables summarize the components of the basic and diluted earnings per common share (“EPS”) computations:

	Years Ended September 30
	2019		2018			2017
	(In millions, except per share amounts)
Basic EPS:
Net income (loss) attributable to Cabot Corporation	$	157	$	(113	)	$	248
Less: Dividends and dividend equivalents to participating securities		1		1			—
Less: Undistributed earnings allocated to participating securities⁽¹⁾		1		—			2
Earnings (loss) allocated to common shareholders (numerator)	$	155	$	(114	)	$	246

Weighted average common shares and participating securities outstanding		59.5		62.4			62.8
Less: Participating securities⁽¹⁾		0.8		0.7			0.5
Adjusted weighted average common shares (denominator)		58.7		61.7			62.3

Per share amounts—basic:
Net income (loss) attributable to Cabot Corporation	$	2.64	$	(1.85	)	$	3.94

Diluted EPS:
Earnings (loss) allocated to common shareholders	$	155	$	(114	)	$	246
Plus: Earnings (loss) allocated to participating securities		2		—			2
Less: Adjusted earnings allocated to participating securities⁽²⁾		2		—			2
Earnings (loss) available to common shares (numerator)	$	155	$	(114	)	$	246

Adjusted weighted average common shares outstanding		58.7		61.7			62.3
Effect of dilutive securities:
Common shares issuable⁽³⁾		0.1		—			0.4
Adjusted weighted average common shares (denominator)		58.8		61.7			62.7

Per share amounts—diluted:
Net income (loss) attributable to Cabot Corporation	$	2.63	$	(1.85	)	$	3.91

⁽¹⁾

Calculation of Undistributed Earnings

	Years Ended September 30
	2019		2018			2017
	(In millions)
Calculation of undistributed earnings:
Net income (loss) attributable to Cabot Corporation	$	157	$	(113	)	$	248
Less: Dividends declared on common stock		80		79			77
Less: Dividends and dividend equivalents to participating securities		1		1			—
Undistributed earnings (loss)	$	76	$	(193	)	$	171
Allocation of undistributed earnings:
Undistributed earnings (loss) allocated to common shareholders	$	75	$	(193	)	$	169
Undistributed earnings allocated to participating securities		1		—			2
Undistributed earnings (loss)	$	76	$	(193	)	$	171

⁽²⁾	^{Undistributed earnings (loss) are adjusted for the assumed distribution of dividends to the dilutive securities, which are described in (3) below, and then reallocated to participating securities.}

⁽³⁾

Income Taxes (Tables)

12 Months Ended

Sep. 30, 2019

Income Tax Disclosure [Abstract]

Income Before Income Taxes

Income from continuing operations before income taxes and equity in net earnings of affiliated companies was as follows:

	Years Ended September 30
	2019			2018			2017
	(In millions)
Domestic	$	(66	)	$	(229	)	$	(8	)
Foreign		321			346			307
Income from continuing operations before income taxes and equity in earnings of affiliated companies	$	255		$	117		$	299

Provision (Benefit) for Income Taxes

Tax provision (benefit) for income taxes consisted of the following:

	Years Ended September 30
	2019			2018			2017
	(In millions)
U.S. federal and state:
Current	$	2		$	14		$	5
Deferred		(30	)		114			(26	)
Total		(28	)		128			(21	)
Foreign:
Current		95			88			59
Deferred		3			(23	)		(5	)
Total		98			65			54
Provision (benefit) for income taxes	$	70		$	193		$	33

Reconciliation Using U.S. Statutory Rate

The provision (benefit) for income taxes differed from the provision for income taxes as calculated using the U.S. statutory rate as follows:

	Years Ended September 30
	2019			2018			2017
	(In millions)
Computed tax expense at the federal statutory rate	$	53		$	29		$	105
Foreign income:
Impact of taxation at different rates, repatriation, losses and other		42			6			(75	)
Impact of increase (decrease) in valuation allowance on deferred taxes		(25	)		(16	)		(7	)
Impact of foreign losses for which a current tax benefit is not available		—			—			1
Impact of non-deductible net currency losses		—			2			—
Impact of the Tax Cuts and Jobs Act of 2017		—			159			—
Global Intangible Low Taxed Income (GILTI)		10			—			—
U.S. and state benefits from research and experimentation activities		(2	)		(2	)		(2	)
Provision (settlement) of unrecognized tax benefits		(8	)		1			7
Impact of goodwill impairment charge		—			18			—
Permanent differences, net		1			(1	)		5
State taxes, net of federal effect		(1	)		(3	)		(1	)
Provision (benefit) for income taxes	$	70		$	193		$	33

Components of Deferred Income Taxes

Significant components of deferred income taxes were as follows:

	September 30
	2019			2018
	(In millions)
Deferred tax assets:
Deferred expenses	$	15		$	17
Intangible assets		28			23
Inventory		9			4
Other		3			4
Pension and other benefits		41			45
Net operating loss carryforwards		124			146
Foreign tax credit carryforwards		20			12
R&D credit carryforwards		43			41
Other business credit carryforwards		29			39
Subtotal		312			331
Valuation allowance		(124	)		(169	)
Total deferred tax assets	$	188		$	162

	September 30
	2019			2018
	(In millions)
Deferred tax liabilities:
Property, plant and equipment	$	(61	)	$	(56	)
Unremitted earnings of non-U.S. subsidiaries		(5	)		(14	)
Total deferred tax liabilities	$	(66	)	$	(70	)

Expiration Dates of Carryforwards

The following table provides detail surrounding the expiration dates of these carryforwards:

Years Ending September 30	NOLs		Credits
	(In millions)
2020 - 2026	$	262	$	40
2027 and thereafter		168		57
Indefinite carryforwards		281		2
Total	$	711	$	99

Reconciliation of Unrecognized Tax Benefits

A reconciliation of the beginning and ending amount of unrecognized tax benefits for fiscal years 2019, 2018 and 2017 is as follows:

	Years Ended September 30
	2019			2018			2017
	(In millions)
Balance at beginning of the year	$	37		$	36		$	30
Additions based on tax provisions related to the current year		—			2			2
Additions for tax positions of prior years		—			1			8
Reductions of tax provisions of prior years		(1	)		—			(1	)
Reductions related to settlements		(5	)		—			(2	)
Reductions from lapse of statute of limitations		(4	)		(2	)		(1	)
Balance at end of the year	$	27		$	37		$	36

Commitments and Contingencies (Tables)

12 Months Ended

Sep. 30, 2019

Commitments And Contingencies Disclosure [Abstract]

Schedule of Future Minimum Rental Commitments under Non-Cancelable Leases

Future minimum rental commitments under non-cancelable leases are as follows:

Years Ending September 30	(In millions)
2020	$	23
2021		14
2022		9
2023		9
2024		8
2025 and thereafter		68
Total future minimum rental commitments	$	131

Schedule of Raw Material Purchased under Long Term Purchase Agreements

	Years Ended September 30
	2019		2018		2017
	(In millions)
Reinforcement Materials	$	393	$	375	$	281
Performance Chemicals		65		55		43
Purification Solutions		8		11		7
Total	$	466	$	441	$	331

Schedule of Components of Purchase Commitments

For these purchase commitments, the amounts included in the table below are based on market prices as of September 30, 2019 which may differ from actual market prices at the time of purchase.

	Payments Due by Fiscal Year
	2020		2021		2022		2023		2024		Thereafter		Total
	(In millions)
Reinforcement Materials	$	218	$	123	$	116	$	108	$	107	$	1,246	$	1,918
Performance Chemicals		57		55		53		35		30		402	$	632
Purification Solutions		6		1		—		—		—		—		7
Total	$	281	$	179	$	169	$	143	$	137	$	1,648	$	2,557

Financial Information by Segment & Geographic Area (Tables)

12 Months Ended

Sep. 30, 2019

Segment Reporting [Abstract]

Schedule of Performance Segment

The net sales from each of these businesses for fiscal 2019, 2018 and 2017 are as follows:

	Years Ended September 30
	2019		2018		2017
	(In millions)
Performance Additives	$	694	$	707	$	650
Formulated Solutions		301		321		258
Total Performance Chemicals	$	995	$	1,028	$	908

Financial Information by Reportable Segment

Financial information by reportable segment is as follows:

Years Ended September 30	Reinforcement Materials			Performance Chemicals		Purification Solutions			Specialty Fluids		Segment Total⁽¹⁾		Unallocated and Other^(2), ⁽⁴⁾			Consolidated Total
	(In millions)
2019
Revenues from external customers⁽³⁾	$	1,815		$	995	$	278		$	56	$	3,144	$	193		$	3,337
Depreciation and amortization	$	69		$	51	$	26		$	1	$	147	$	1		$	148
Equity in earnings of affiliated companies	$	(1	)	$	1	$	3		$	—	$	3	$	(2	)	$	1
Income (loss) from continuing operations before income taxes⁽⁴⁾	$	266		$	152	$	2		$	24	$	444	$	(189	)	$	255
Assets⁽⁵⁾	$	1,177		$	1,024	$	436		$	—	$	2,637	$	367		$	3,004
Total expenditures for additions to long-lived assets⁽⁶⁾	$	82		$	148	$	11		$	1	$	242	$	5		$	247
2018
Revenues from external customers⁽³⁾	$	1,774		$	1,028	$	279		$	45	$	3,126	$	116		$	3,242
Depreciation and amortization	$	70		$	48	$	32		$	2	$	152	$	(3	)	$	149
Equity in earnings of affiliated companies	$	1		$	—	$	6		$	—	$	7	$	(5	)	$	2
Income (loss) from continuing operations before income taxes⁽⁴⁾	$	279		$	200	$	(7	)	$	8	$	480	$	(363	)	$	117
Assets⁽⁵⁾	$	1,319		$	919	$	460		$	178	$	2,876	$	368		$	3,244
Total expenditures for additions to long-lived assets⁽⁶⁾	$	97		$	94	$	16		$	17	$	224	$	5		$	229
2017
Revenues from external customers⁽³⁾	$	1,381		$	908	$	281		$	41	$	2,611	$	106		$	2,717
Depreciation and amortization	$	69		$	46	$	39		$	2	$	156	$	(1	)	$	155
Equity in earnings of affiliated companies	$	6		$	—	$	6		$	—	$	12	$	(5	)	$	7
Income (loss) from continuing operations before income taxes⁽⁴⁾	$	193		$	201	$	6		$	9	$	409	$	(110	)	$	299
Assets⁽⁵⁾	$	1,189		$	708	$	741		$	140	$	2,778	$	560		$	3,338
Total expenditures for additions to long-lived assets⁽⁶⁾	$	68		$	47	$	19		$	5	$	139	$	8		$	147

⁽¹⁾	Cabot divested its Specialty Fluids business on June 28, 2019. Refer to Note D for the terms of this transaction.

⁽²⁾	Unallocated and Other includes certain items and eliminations necessary to reflect management’s reporting of operating segment results. These items are reflective of the segment reporting presented to the CODM.

⁽³⁾

	Years Ended September 30
	2019			2018		2017
	(In millions)
Royalties, the impact of unearned revenue, the removal of 100% of the sales of an equity method affiliate and discounting charges for certain Notes receivable	$	(13	)	$	11	$	11
Shipping and handling fees		130			105		95
By-product sales^(a)		76			—		—
Total	$	193		$	116	$	106

^(a)

⁽⁴⁾

	Years Ended September 30
	2019			2018			2017
	(In millions)
Interest expense	$	(59	)	$	(54	)	$	(53	)
Certain items:^(a)
Specialty Fluids loss on sale and asset impairment charge (Note D)		(29	)		—			—
Legal and environmental matters and reserves		(21	)		(16	)		1
Global restructuring activities (Note P)		(16	)		30			(3	)
Equity affiliate investment impairment charge (Note M)		(11	)		—			—
Acquisition and integration-related charges		(6	)		(2	)		—
Executive transition costs		(1	)		(2	)		—
Purification Solutions goodwill and long-lived assets impairment charge (Note G)		—			(254	)		—
Inventory reserve adjustment		—			(13	)		—
Gains (losses) on sale of investments		—			10			—
Other certain items		(3	)		(1	)		(1	)
Total certain items, pre-tax		(87	)		(248	)		(3	)
Unallocated corporate costs^(b)		(50	)		(61	)		(50	)
General unallocated income (expense)^(c)		8			2			3
Less: Equity in earnings of affiliated companies, net of tax^(d)		1			2			7
Total	$	(189	)	$	(363	)	$	(110	)

^(a)

Certain items are items that management does not consider representative of operating segment results and they are, therefore, excluded from Segment EBIT.

^(b)

Unallocated corporate costs are not controlled by the segments and primarily benefit corporate interests.

^(c)

^(d)

Equity in earnings of affiliated companies, net of tax is included in Segment EBIT and is removed from Unallocated and other to reconcile to income (loss) from operations before taxes.

⁽⁵⁾	Unallocated and Other assets includes cash, marketable securities, cost investments, income taxes receivable, deferred taxes, headquarters’ assets, and current and non-current assets held for sale.

⁽⁶⁾	Expenditures for additions to long-lived assets include total equity and other investments (including available-for-sale securities) and property, plant and equipment.

Revenues from External Customers and Long-Lived Asset Information by Geographic Area

	Years Ended September 30
	2019		2018		2017
	(In millions)
United States	$	702	$	676	$	645
China		738		752		573
Other countries		1,897		1,814		1,499
Total	$	3,337	$	3,242	$	2,717

Long-lived assets attributable to an individual country, other than the U.S. and China, were not material for disclosure. Long-lived asset information by individual country is summarized as follows:

	Years Ended September 30
	2019		2018		2017
	(In millions)
United States	$	572	$	493	$	493
China		264		270		261
Other countries		512		533		551
Total	$	1,348	$	1,296	$	1,305

Revenues from External Customers by Geographic Region

	Year Ended September 30, 2019
	Reinforcement Materials		Performance Chemicals		Purification Solutions		Specialty Fluids		Consolidated Total
	(In millions)
Americas	$	688	$	294	$	126	$	6	$	1,114
Asia Pacific		769		353		35		1		1,158
Europe, Middle East and Africa		358		348		117		49		872
Segment revenues from external customers		1,815		995		278		56		3,144
Unallocated and other										193
Net sales and other operating revenues									$	3,337

Unaudited Quarterly Financial Information (Tables)

12 Months Ended

Sep. 30, 2019

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information

Unaudited financial results by quarter for fiscal 2019 and 2018 are summarized below:

	Quarters Ended								Year Ended
	December 31,		March 31,		June 30,		September 30,		September 30,
	2018		2019		2019		2019		2019
	(In millions, except per share amounts)
Net sales and other operating revenues	$	821	$	844	$	845	$	827	$	3,337
Gross profit	$	166	$	178	$	170	$	171	$	685
Net income (loss)	$	77	$	29	$	40	$	40	$	186
Net income (loss) attributable to Cabot Corporation	$	69	$	23	$	32	$	33	$	157
Earnings per common share—basic	$	1.14	$	0.39	$	0.55	$	0.56	$	2.64
Earnings per common share—diluted	$	1.14	$	0.39	$	0.55	$	0.55	$	2.63

	Quarters Ended										Year Ended
	December 31,			March 31,			June 30,		September 30,		September 30,
	2017			2018			2018		2018		2018
	(In millions, except per share amounts)
Net sales and other operating revenues	$	720		$	818		$	854	$	850	$	3,242
Gross profit	$	176		$	188		$	197	$	211	$	772
Net income (loss)	$	(112	)	$	(163	)	$	99	$	102	$	(74	)
Net income (loss) attributable to Cabot Corporation	$	(122	)	$	(173	)	$	88	$	94	$	(113	)
Earnings per common share—basic	$	(1.98	)	$	(2.80	)	$	1.41	$	1.51	$	(1.85	)
Earnings per common share—diluted	$	(1.98	)	$	(2.80	)	$	1.40	$	1.51	$	(1.85	)

Significant Accounting Policies - Additional Information (Detail) ¥ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2019 CNY (¥)	Sep. 30, 2018 CNY (¥)
Significant Accounting Policies [Line Items]
Equity affiliate investments	$ 39,000,000		$ 39,000,000	$ 52,000,000
Changed date of annual impairment test	August 31
Reason for change in date of annual goodwill impairment test			This date is preferred as it better aligns with the Company’s planning process, which produces a significant input to the testing, and it did not result in a material change to the Company’s consolidated financial statements.
Capitalized interest			$ 4,000,000	2,000,000	$ 1,000,000
Asset retirement obligation reserve	$ 26,000,000		26,000,000	28,000,000
Charges on sale of notes receivables			3,000,000	3,000,000	2,000,000
Changes in allowance			$ 0	0
Chance of utilizing the associated benefit for valuation allowances, maximum			50.00%
Accounts Payable and Accrued Liabilities [Member]
Significant Accounting Policies [Line Items]
Capital expenditures			$ 23,000,000	29,000,000	7,000,000
Equity Method Investments [Member]
Significant Accounting Policies [Line Items]
Dividends declared			$ 4,000,000	9,000,000	11,000,000
Minimum [Member]
Significant Accounting Policies [Line Items]
Payment terms			0 days
Minimum [Member] \| Buildings [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment			20 years
Minimum [Member] \| Machinery and Equipment [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment			10 years
Minimum [Member] \| Other Fixed Assets [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment			3 years
Minimum [Member] \| Cabot [Member]
Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage	20.00%		20.00%			20.00%
Maximum [Member]
Significant Accounting Policies [Line Items]
Payment terms			90 days
Maximum [Member] \| Buildings [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment			25 years
Maximum [Member] \| Machinery and Equipment [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment			25 years
Maximum [Member] \| Other Fixed Assets [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment			25 years
Maximum [Member] \| Cabot [Member]
Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage	50.00%		50.00%			50.00%
Other Nonoperating Income (Expense) [Member]
Significant Accounting Policies [Line Items]
Foreign currency transaction gains (losses)				(4,000,000)	$ (4,000,000)
Other Nonoperating Income (Expense) [Member] \| Maximum [Member]
Significant Accounting Policies [Line Items]
Foreign currency transaction gains (losses)			$ 1,000,000
Venezuela [Member] \| Carbon Black Affiliate [Member]
Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage		49.00%
Venezuela [Member] \| Carbon Black Affiliate [Member] \| Other Nonoperating Income (Expense) [Member]
Significant Accounting Policies [Line Items]
Impairment charge		$ 11,000,000
China [Member]
Significant Accounting Policies [Line Items]
Accounts and notes receivable, net	$ 4,000,000		$ 4,000,000	$ 5,000,000		¥ 30	¥ 32

Recent Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Oct. 01, 2019
Significant Accounting Policies [Line Items]
Net sales and other operating revenues	$ 827	$ 845	$ 844	$ 821	$ 850	$ 854	$ 818	$ 720		$ 3,337	$ 3,242	$ 2,717
Cost of sales										$ 2,652	$ 2,470	$ 2,060
Subsequent Event [Member] \| Minimum [Member]
Significant Accounting Policies [Line Items]
Right of use asset													$ 100
Lease payable obligation													100
Subsequent Event [Member] \| Maximum [Member]
Significant Accounting Policies [Line Items]
Right of use asset													120
Lease payable obligation													$ 120
Difference between Revenue Guidance in Effect before and after Topic 606
Significant Accounting Policies [Line Items]
Net sales and other operating revenues									$ (76)
Cost of sales									$ (76)

Recent Accounting Pronouncements - Schedule of Change Retrospectively to Prior Periods Consolidated Statements of Operations (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Significant Accounting Policies [Line Items]
Cost of sales									$ 2,652	$ 2,470	$ 2,060
Gross profit	$ 171	$ 170	$ 178	$ 166	$ 211	$ 197	$ 188	$ 176	685	772	657
Selling and administrative expenses									290	308	262
Research and technical expenses									60	66	57
Income (loss) from operations									306	144	338
Other income (expense)									$ (1)	17	5
Change in Method of Accounting for Inventories from Last-in, First-out Method to First-in, First-out Method [Member]
Significant Accounting Policies [Line Items]
Cost of sales										2,470	2,060
Gross profit										772	657
Selling and administrative expenses										308	262
Research and technical expenses										66	57
Income (loss) from operations										144	338
Other income (expense)										17	5
Change in Method of Accounting for Inventories from Last-in, First-out Method to First-in, First-out Method [Member] \| As Originally Reported [Member]
Significant Accounting Policies [Line Items]
Cost of sales										2,461	2,054
Gross profit										781	663
Selling and administrative expenses										305	260
Research and technical expenses										66	56
Income (loss) from operations										156	347
Other income (expense)										5	(4)
Change in Method of Accounting for Inventories from Last-in, First-out Method to First-in, First-out Method [Member] \| Effect of Change [Member]
Significant Accounting Policies [Line Items]
Cost of sales										9	6
Gross profit										(9)	(6)
Selling and administrative expenses										3	2
Research and technical expenses											1
Income (loss) from operations										(12)	(9)
Other income (expense)										$ 12	$ 9

Acquisitions - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended			12 Months Ended
	Jun. 30, 2019	Sep. 30, 2018	Nov. 30, 2017	Sep. 30, 2019
Tech Blend [Member]
Business Acquisition [Line Items]
Acquisition date			Nov. 30, 2017
Business acquisition, purchase price			$ 65
NSCC Carbon (Jiangsu) Co. Ltd [Member]
Business Acquisition [Line Items]
Acquisition date		Sep. 30, 2018
Expected production commencement year		2021
Transition related costs				$ 4
NSCC Carbon (Jiangsu) Co. Ltd [Member] \| Accounts Payable and Accrued Liabilities [Member]
Business Acquisition [Line Items]
Business acquisition, purchase price		$ 8
Other Acquisition [Member] \| Intangible Assets [Member]
Business Acquisition [Line Items]
Business acquisition, purchase price	$ 3

Sale of the Specialty Fluids Business - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2019
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total proceeds from sale of Specialty Fluids business			$ 135
Impairment charge			29
Sinomine (Hong Kong) Rare Metals Resources Co. Limited [Member] \| Specialty Fluids [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Total proceeds from sale of Specialty Fluids business	$ 133
Amount of cash transferred	2
Pre-tax loss on sale of Specialty Fluids business			$ 9
Impairment charge		$ 20
Additional cash royalties for lithium products	$ 5
Royalty payable term	10 years

Inventories - Components of Company's Inventories (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Inventory Disclosure [Abstract]
Raw materials	$ 107	$ 129
Work in process		3
Finished goods	305	329
Other	54	50
Total	$ 466	$ 511

Inventories - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Inventory Disclosure [Abstract]
Obsolete inventory reserve	$ 29	$ 38
Lower of cost or market charge inventory		$ 13

Property, Plant and Equipment - Components of Property, Plant and Equipment (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Property Plant And Equipment [Abstract]
Land and land improvements	$ 144	$ 142
Buildings	524	514
Machinery and equipment	2,369	2,373
Other	247	249
Construction in progress	262	242
Total property, plant and equipment	3,546	3,520
Less: Accumulated depreciation	(2,198)	(2,224)
Net property, plant and equipment	$ 1,348	$ 1,296	$ 1,305

Property, Plant and Equipment - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Property Plant And Equipment [Abstract]
Depreciation expense	$ 142	$ 142	$ 147

Purification Solutions Goodwill and Long-Lived Assets Impairment Charges - Impairment Charges and Associated Tax Benefit (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Goodwill And Intangible Assets [Line Items]
Purification Solutions goodwill impairment charge			$ 92
Purification Solutions long-lived assets impairment charge			162
Benefit for income taxes		$ (27)	$ 91	$ (31)
Impairment charges, after tax		$ 29
Purification Solutions [Member]
Goodwill And Intangible Assets [Line Items]
Purification Solutions goodwill impairment charge	$ 92
Purification Solutions long-lived assets impairment charge	162
Benefit for income taxes	(30)
Impairment charges, after tax	$ 224

Purification Solutions Goodwill and Long-Lived Assets Impairment Charges - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2018
Goodwill And Intangible Assets [Line Items]
Goodwill impairment charge			$ 92
Lower of cost or market reserve inventory	$ 13		13
Long-lived assets impairment charge			$ 162
Assets impairment charges income tax benefit		$ 30
Reducing of impairment charges and restructuring costs	$ 1
Purification Solutions [Member]
Goodwill And Intangible Assets [Line Items]
Goodwill impairment charge		92
Lower of cost or market reserve inventory		13
Long-lived assets impairment charge		162
Impairment charges of definite lived Intangible assets		64
Purification Solutions [Member] \| Property, Plant and Equipment [Member]
Goodwill And Intangible Assets [Line Items]
Long-lived assets impairment charge		$ 98

Goodwill and Intangible Assets - Schedule of Goodwill Balances (Detail) $ in Millions	12 Months Ended
	Sep. 30, 2019 USD ($)
Goodwill And Intangible Assets [Line Items]
Beginning balance	$ 93
Foreign currency impact	(3)
Ending balance	90
Reinforcement Materials [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	52
Foreign currency impact	(2)
Ending balance	50
Performance Chemicals [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	41
Foreign currency impact	(1)
Ending balance	$ 40

Goodwill and Intangible Assets - Schedule of Goodwill Balances (Parenthetical) (Detail) - USD ($)	Sep. 30, 2019	Sep. 30, 2018
Purification Solutions [Member]
Goodwill And Intangible Assets [Line Items]
Accumulated impairment losses	$ 444,000,000	$ 444,000,000
Reinforcement Materials [Member]
Goodwill And Intangible Assets [Line Items]
Accumulated impairment losses	$ 0	$ 0

Goodwill and Intangible Assets - Schedule of Intangible Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	$ 115	$ 111
Accumulated Amortization	(19)	(13)
Net Intangible Assets, finite lives	96	98
Developed Technologies [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	50	52
Accumulated Amortization	(5)	(2)
Net Intangible Assets, finite lives	45	50
Trademarks [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	8	8
Net Intangible Assets, finite lives	8	8
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	57	51
Accumulated Amortization	(14)	(11)
Net Intangible Assets, finite lives	$ 43	$ 40

Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Goodwill And Intangible Assets [Line Items]
Amortization expense estimated for year one	$ 6
Amortization expense estimated for year two	6
Amortization expense estimated for year three	6
Amortization expense estimated for year four	6
Amortization expense estimated for year five	6
Cost of Sales, Selling and Administrative Expenses and Research and Technical Expenses [Member]
Goodwill And Intangible Assets [Line Items]
Amortization of intangible assets	$ 6	$ 7	$ 8
Minimum [Member]
Goodwill And Intangible Assets [Line Items]
Useful life of intangible assets	12 years
Maximum [Member]
Goodwill And Intangible Assets [Line Items]
Useful life of intangible assets	25 years
Weighted Average [Member]
Goodwill And Intangible Assets [Line Items]
Useful life of intangible assets	19 years

Accounts Payable, Accrued Liabilities and Other Liabilities - Components of Accounts Payable and Accrued Liabilities (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Payables And Accruals [Abstract]
Accounts payable	$ 390	$ 446
Accrued employee compensation	51	70
Other accrued liabilities	96	97
Total	$ 537	$ 613

Accounts Payable, Accrued Liabilities and Other Liabilities - Components of Other Long-Term Liabilities (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Payables And Accruals [Abstract]
Employee benefit plan liabilities	$ 91	$ 118
Non-current tax liabilities	12	19
Other accrued liabilities	103	115
Total	$ 206	$ 252

Debt and Other Obligations - Schedule of Long-Term Obligations (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Total variable rate debt	$ 99	$ 90
Total Medium Term Notes	23	53
Debt	1,026
Total debt	927	657
Capital lease obligations, due through fiscal 2033	12	11
Unamortized debt issuance costs and debt discount	(7)	(4)
Total debt	1,031	754
Less current portion of long-term debt	(7)	(35)
Total long-term debt	1,024	719
Revolving Credit Facility - Canada, expires fiscal 2021 [Member]
Debt Instrument [Line Items]
Line of credit	43	90
Revolving Credit Facility - Euro, expires fiscal 2024 [Member]
Debt Instrument [Line Items]
Line of credit	56
Notes matured fiscal 2019, 7.42% [Member]
Debt Instrument [Line Items]
Total Medium Term Notes		30
3.7% Notes due fiscal 2022 [Member]
Debt Instrument [Line Items]
Notes	350	350
3.4% Notes due fiscal 2026 [Member]
Debt Instrument [Line Items]
Notes	250	250
Notes due fiscal 2022, 8.34% - 8.47% [Member]
Debt Instrument [Line Items]
Total Medium Term Notes	15	15
Notes due fiscal 2028, 6.57% - 7.28% [Member]
Debt Instrument [Line Items]
Total Medium Term Notes	8	8
4.0% Notes due fiscal 2029 [Member]
Debt Instrument [Line Items]
Notes	300
Chinese Renminbi Debt, Due Fiscal 2020, 4.35% [Member]
Debt Instrument [Line Items]
Debt	$ 4
Chinese Renminbi Debt, Matured Fiscal 2019, 4.35% [Member]
Debt Instrument [Line Items]
Debt		$ 4

Debt and Other Obligations - Schedule of Long-Term Obligations (Parenthetical) (Detail)	1 Months Ended	12 Months Ended
	Jun. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Revolving Credit Facility, expires fiscal 2023 [Member]
Debt Instrument [Line Items]
Debt instrument due, year		2023	2023
Revolving Credit Facility - Canada, expires fiscal 2021 [Member]
Debt Instrument [Line Items]
Debt instrument due, year		2021	2021
Revolving Credit Facility - Euro, expires fiscal 2024 [Member]
Debt Instrument [Line Items]
Debt instrument due, year		2024	2024
3.7% Notes due fiscal 2022 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		3.70%	3.70%
Debt instrument due, year		2022	2022
3.4% Notes due fiscal 2026 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		3.40%	3.40%
Debt instrument due, year		2026	2026
4.0% Notes due 2029 [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate	4.00%	4.00%	4.00%
Debt instrument due, year	2029	2029	2029
Notes matured fiscal 2019, 7.42% [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		7.42%	7.42%
Debt instrument due, year		2019	2019
Notes due fiscal 2022, 8.34% - 8.47% [Member]
Debt Instrument [Line Items]
Debt instrument due, year		2022	2022
Notes due fiscal 2022, 8.34% - 8.47% [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		8.34%	8.34%
Notes due fiscal 2022, 8.34% - 8.47% [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		8.47%	8.47%
Notes due fiscal 2028, 6.57% - 7.28% [Member]
Debt Instrument [Line Items]
Debt instrument due, year		2028	2028
Notes due fiscal 2028, 6.57% - 7.28% [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		6.57%	6.57%
Notes due fiscal 2028, 6.57% - 7.28% [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		7.28%	7.28%
Chinese Renminbi Debt, Due Fiscal 2020, 4.35% [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		4.35%	4.35%
Debt instrument due, year		2020	2020
Chinese Renminbi Debt, Matured Fiscal 2019, 4.35% [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate		4.35%	4.35%
Debt instrument due, year		2019	2019
Capital Lease Obligations, Due Through 2033 [Member]
Debt Instrument [Line Items]
Debt instrument maturity, maximum range		2033	2033

Debt and Other Obligations - Additional Information (Detail)	1 Months Ended					12 Months Ended
	Jun. 30, 2019 USD ($)	Nov. 30, 2018 USD ($)	Sep. 30, 2016 USD ($)	Nov. 30, 2013 USD ($)	Jul. 31, 2012 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	May 31, 2019 EUR (€)	Oct. 31, 2015 USD ($)
Debt Instrument [Line Items]
Revolving credit facility, committed amount						$ 1,000,000,000
Long-term debt						1,026,000,000
Unsecured medium term notes outstanding issued						$ 23,000,000	$ 53,000,000
Maturity of the total outstanding medium term notes, years						5 years
Weighted average interest of medium term notes						7.96%
Capital lease obligations						$ 12,000,000	11,000,000
Repayments of long-term capital lease obligations						$ 21,000,000
Repayment period of capital lease obligation, years						14 years
Payment towards imputed interest						$ 9,000,000
Original cost of capital lease assets						20,000,000	20,000,000
Accumulated depreciation of assets under capital leases						13,000,000	13,000,000
Short-term borrowings						33,000,000	249,000,000
NHUMO [Member]
Debt Instrument [Line Items]
Preferred stock repurchase amount		$ 25,000,000		$ 25,000,000
Dividend percentage of preferred stock				6.00%
Preferred stock dividend		$ 1,400,000
Commercial Paper [Member]
Debt Instrument [Line Items]
Short-term borrowings						$ 33,000,000	$ 249,000,000
Weighted-average interest rate						2.27%	2.36%
Short-term Notes Payable [Member]
Debt Instrument [Line Items]
Short-term borrowings						$ 0	$ 0
Chinese Renminbi Debt [Member]
Debt Instrument [Line Items]
Long-term debt						$ 4,000,000	$ 4,000,000
2.55% Notes Due 2018 [Member]
Debt Instrument [Line Items]
Debt maturity date						Jan. 15, 2018
Registered unsecured notes issued					$ 250,000,000
Debt instrument, discount					$ 1,000,000
Proceeds from issuance of unsecured notes						$ 248,000,000
2.55% Notes Due 2018 [Member] \| Fixed Rate Debt [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate					2.55%
Debt instrument due, year						2018
3.7% Notes due fiscal 2022 [Member]
Debt Instrument [Line Items]
Debt maturity date						Jul. 15, 2022
Debt instrument, interest rate						3.70%	3.70%
Registered unsecured notes issued					$ 350,000,000
Debt instrument, discount					$ 1,000,000
Proceeds from issuance of unsecured notes						$ 347,000,000
Debt instrument due, year						2022	2022
3.7% Notes due fiscal 2022 [Member] \| Fixed Rate Debt [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate					3.70%
Debt instrument due, year						2022
3.4% Notes due fiscal 2026 [Member]
Debt Instrument [Line Items]
Debt maturity date						Sep. 15, 2026
Debt instrument, interest rate						3.40%	3.40%
Registered unsecured notes issued			$ 250,000,000
Debt instrument, discount			$ 1,000,000
Proceeds from issuance of unsecured notes						$ 248,000,000
Debt instrument due, year						2026	2026
3.4% Notes due fiscal 2026 [Member] \| Fixed Rate Debt [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate			3.40%
Debt instrument due, year						2026
4.0% Notes due 2029 [Member]
Debt Instrument [Line Items]
Debt issuance cost	$ 3,000,000
Debt maturity date	Jul. 01, 2029
Debt instrument, interest rate	4.00%					4.00%	4.00%
Registered unsecured notes issued	$ 300,000,000
Debt instrument, discount	1,000,000
Proceeds from issuance of unsecured notes	$ 296,000,000
Debt instrument due, year	2029					2029	2029
Revolving Credit Facility, expires fiscal 2023 [Member]
Debt Instrument [Line Items]
Amount available under credit facility						$ 967,000,000
Revolving credit facility, committed amount									$ 1,000,000,000
Debt instrument, maturity date						Oct. 23, 2022
Debt instrument due, year						2023	2023
Revolving Credit Facility - Canada, expires fiscal 2021 [Member]
Debt Instrument [Line Items]
Revolving credit facility, committed amount							$ 100,000,000
Debt instrument, maturity date						Sep. 24, 2021
Credit agreement, available borrowing						$ 57,000,000
Revolving credit facility, weighted average interest rate						3.21%
Debt instrument due, year						2021	2021
Revolving Credit Facility - Euro, expires fiscal 2024 [Member]
Debt Instrument [Line Items]
Revolving credit facility, committed amount \| €								€ 300,000,000
Debt instrument, maturity date						May 22, 2024
Credit agreement, available borrowing						$ 272,000,000
Revolving credit facility, weighted average interest rate						3.42%
Debt issuance cost						$ 1,000,000
Debt instrument due, year						2024	2024
Standby Letters of Credit [Member]
Debt Instrument [Line Items]
Debt instrument due, year						2020
Standby letters of credit, outstanding amount						$ 5,000,000

Debt and Other Obligations - Schedule of Future Years Payment (Detail) $ in Millions	Sep. 30, 2019 USD ($)
Debt Disclosure [Abstract]
2020	$ 4
2021	43
2022	365
2024	56
Thereafter	558
Total	1,026
2020	3
2021	3
2022	3
2023	3
2024	2
Thereafter	7
Less: Interest	(9)
Total	12
2020	7
2021	46
2022	368
2023	3
2024	58
Thereafter	565
Total	$ 1,038

Financial Instruments and Fair Value Measurements - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, liabilities, Level 2 to Level 1 transfers, amount	$ 0	$ 0
Fair value, assets, Level 2 to Level 1 transfers, amount	0	0
Fair value, liabilities, Level 1 to Level 2 transfers, amount	0	0
Fair value, assets, Level 1 to Level 2 transfers, amount	0	0
Fair value, assets, transfers into Level 3, amount	0	0
Fair value, assets, transfers out of Level 3, amount	0	0
Fair value, liabilities, transfers into Level 3, amount	0	0
Fair value, liabilities, transfers out of Level 3, amount	0	0
Fair value of long-term debt	1,095,000,000	742,000,000
Fixed Rate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of long-term debt	1,026,000,000	747,000,000
Significant Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets in the Consolidated Balance Sheets	10,000,000	11,000,000
Significant Observable Inputs (Level 2) [Member] \| Foreign Currency Risks [Member] \| Prepaid Expenses and Other Current Assets and Other Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets (liabilities), at fair Value, net	$ 1,000,000	$ (18,000,000)

Derivatives - Additional Information (Detail)	12 Months Ended
Derivatives - Additional Information (Detail)	Sep. 30, 2019 USD ($) Derivative	Sep. 30, 2018 USD ($) Derivative
Derivative [Line Items]
Significant concentration of credit risk associated with our derivative instruments	$ 0	$ 0
Cross Currency Swaps [Member] \| Prepaid Expenses And Other Asset Current And Other Assets [Member]
Derivative [Line Items]
Fair value of swaps, net asset	$ 1,000,000
Cross Currency Swaps [Member] \| Prepaid Expenses And Other Asset Current And Other Liabilities [Member]
Derivative [Line Items]
Fair value of swaps, net liability		$ 18,000,000
Fair Value Hedging [Member] \| Interest Rate Swap-Fixed to Variable [Member] \| Interest Rate Risk [Member]
Derivative [Line Items]
Derivatives held to manage interest rate risk \| Derivative	0	0
Net Investment Hedge [Member] \| Cross Currency Swaps [Member]
Derivative [Line Items]
Notional Amount	$ 250,000,000
Net cash interest received	4,000,000	$ 3,000,000
Cumulative gain (loss) related to swaps	$ 5,000,000	$ (14,000,000)
Net Investment Hedge [Member] \| Cross Currency Swaps [Member] \| Fixed Rate Debt [Member]
Derivative [Line Items]
Derivative Instruments Frequency of Cash Settlements	semi-annually

Derivatives - Details of Derivatives Held to Manage Foreign Currency Risk (Detail)

Sep. 30, 2019

USD ($)

Sep. 30, 2019

EUR (€)

Sep. 30, 2018

USD ($)

Sep. 30, 2018

EUR (€)

Sep. 30, 2016

3.4% Notes [Member]

Derivative [Line Items]

Interest rate on borrowing

3.40%

3.4% Notes [Member] | Fixed Rate Debt [Member]

Derivative [Line Items]

Interest rate on borrowing

3.40%

Net Investment Hedge [Member] | Cross Currency Swaps [Member]

Derivative [Line Items]

Notional Amount

$ 250,000,000

Net Investment Hedge [Member] | 3.4% Notes [Member] | Cross Currency Swaps [Member]

Derivative [Line Items]

Notional Amount

$ 250,000,000

€ 223,000,000

$ 250,000,000

€ 223,000,000

Net Investment Hedge [Member] | 3.4% Notes [Member] | Fixed Rate Debt [Member] | Cross Currency Swaps [Member]

Derivative [Line Items]

Interest rate on borrowing

3.40%

Not Designated as Hedging Instrument [Member] | Forward Foreign Currency Contracts [Member]

Derivative [Line Items]

Notional Amount

^[1]

$ 54,000,000

$ 18,000,000

[1]	Cabot’s forward foreign exchange contracts are denominated in British pound, Canadian dollar, Indonesian rupiah and Czech koruna.

Derivatives - Summary Impact of Cross-currency Swaps to AOCI and Consolidated Statements of Operations (Detail) - Cross Currency Swaps [Member] - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Derivative Instruments Gain Loss [Line Items]
Gain/(Loss) Recognized in AOCI	$ 23	$ (2)	$ (10)
(Gain)/Loss Reclassified from AOCI into Interest Expense in the Consolidated Statements of Operations	(5)	(5)
(Gain)/Loss Recognized in Interest Expense in the Consolidated Statements of Operations (Amount Excluded from Effectiveness Testing)	$ 1	$ 2

Hyperinflationary Economies - Additional Information (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($)	Sep. 30, 2019 USD ($) $ / $	Sep. 30, 2018 USD ($) $ / $	Sep. 30, 2017 USD ($)
Other Nonoperating Income (Expense) [Member]
Schedule Of Equity Method Investments [Line Items]
Foreign currency transaction gains (losses)			$ (4)	$ (4)
Maximum [Member] \| Other Nonoperating Income (Expense) [Member]
Schedule Of Equity Method Investments [Line Items]
Foreign currency transaction gains (losses)		$ 1
Argentina [Member]
Schedule Of Equity Method Investments [Line Items]
Percentage of net revenue		3.00%	2.00%
Foreign currency exchange rate, translation \| $ / $		57.32	39.70
Argentina [Member] \| Other Nonoperating Income (Expense) [Member]
Schedule Of Equity Method Investments [Line Items]
Foreign currency transaction gains (losses)		$ 2	$ 3
Argentina [Member] \| Maximum [Member]
Schedule Of Equity Method Investments [Line Items]
Percentage of assets and liabilities current		2.00%	2.00%
Venezuela [Member] \| Carbon Black Affiliate [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	49.00%
Venezuela [Member] \| Other Nonoperating Income (Expense) [Member] \| Carbon Black Affiliate [Member]
Schedule Of Equity Method Investments [Line Items]
Impairment charge	$ 11
Carbon Black Operating Entity [Member] \| Argentina [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		100.00%

Employee Benefit Plans - Additional Information (Detail)	3 Months Ended		12 Months Ended
	Sep. 30, 2019 USD ($) Plan	Jun. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($) Plan	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plans expenses				$ 20,000,000	$ 19,000,000	$ 18,000,000
Number of foreign defined benefit plans \| Plan	1			1
Reduction in net pension obligations				$ 30,000,000
Pre-tax gain from net pension obligations	$ 7,000,000			7,000,000
Additional charge on defined benefit plan actuarial gain (loss)				$ 3,000,000
Pay out period for additional charge payment				5 years
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Net losses on curtailments and settlements					(1,000,000)	$ (1,000,000)
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected contribution	10,000,000			$ 10,000,000
Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Net loss amortized from AOCI to net periodic benefit cost			$ 3,000,000
Amortization of estimated prior service credits			0
Scenario, Forecast [Member] \| Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement medical benefits			$ 4,000,000
U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	157,000,000			$ 157,000,000	143,000,000
Gain on settlements	$ 13,000,000
Weighted-average assumed health care cost trend rate	6.50%			6.50%
U.S. Defined Benefit Plans [Member] \| Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				32.00%
U.S. Defined Benefit Plans [Member] \| Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				68.00%
U.S. Defined Benefit Plans [Member] \| Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
One percentage point change effect on postretirement benefit obligation				$ 1,000,000
U.S. Defined Benefit Plans [Member] \| Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax gain from net pension obligations	$ (13,000,000)			(13,000,000)	1,000,000
Net losses on curtailments and settlements				(1,000,000)	(5,000,000)
U.S. Defined Benefit Plans [Member] \| Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax gain from net pension obligations	6,000,000			6,000,000	7,000,000
Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation	$ 205,000,000			$ 205,000,000	349,000,000
Weighted-average assumed health care cost trend rate	6.90%			6.90%
One percentage point change effect on postretirement benefit obligation				$ 3,000,000
Foreign Plans [Member] \| Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				49.00%
Foreign Plans [Member] \| Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				41.00%
Foreign Plans [Member] \| Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				6.00%
Foreign Plans [Member] \| Cash and Other Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				4.00%
Foreign Plans [Member] \| Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax gain from net pension obligations	$ (36,000,000)			$ (36,000,000)	(49,000,000)
Net losses on curtailments and settlements				(134,000,000)	(2,000,000)
Gain on settlements				7,000,000
Foreign Plans [Member] \| Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax gain from net pension obligations	$ (6,000,000)			$ (6,000,000)	$ (4,000,000)
U.K. Plan [Member] \| Other Nonoperating Income (Expense) [Member]
Defined Benefit Plan Disclosure [Line Items]
Charge on effect of accued benefit		$ 2,000,000

Employee Benefit Plans - Change in Projected Benefit Obligations and Change in Plan Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Change in Plan Assets:
Fair value of plan assets at beginning of year	$ 472
Fair value of plan assets at end of year	346	$ 472
Pension Benefits [Member] \| U.S. Defined Benefit Plans [Member]
Change in Benefit Obligations:
Benefit obligation at beginning of year	143	160
Service cost	1	1	$ 1
Interest cost	5	5	4
(Gain) Loss from changes in actuarial assumptions and plan experience	21	(10)
Benefits paid	(11)	(7)
Settlements or curtailments	(1)	(5)
Other	(1)	(1)
Benefit obligation at end of year	157	143	160
Change in Plan Assets:
Fair value of plan assets at beginning of year	149	156
Actual return on plan assets	14	4
Employer contribution	1	1
Benefits paid	(11)	(7)
Settlements	(1)	(4)
Expenses paid from assets	(1)	(1)
Fair value of plan assets at end of year	151	149	156
Funded status	(6)	6
Recognized asset (liability)	(6)	6
Pension Benefits [Member] \| Foreign Plans [Member]
Change in Benefit Obligations:
Benefit obligation at beginning of year	373	376
Service cost	7	9	10
Interest cost	5	7	6
Plan participants’ contribution	1	2
Foreign currency exchange rate changes	(13)	(7)
(Gain) Loss from changes in actuarial assumptions and plan experience		2
Benefits paid	(7)	(13)
Settlements or curtailments	(134)	(2)
Divestiture of Specialty Fluids	(13)
Other	1	(1)
Benefit obligation at end of year	220	373	376
Change in Plan Assets:
Fair value of plan assets at beginning of year	323	318
Actual return on plan assets	17	17
Employer contribution	7	9
Plan participants’ contribution	1	2
Foreign currency exchange rate changes	(11)	(7)
Benefits paid	(7)	(13)
Settlements	(124)	(2)
Divestiture	(10)
Expenses paid from assets	(1)	(1)
Fair value of plan assets at end of year	195	323	318
Funded status	(25)	(50)
Recognized asset (liability)	(25)	(50)
Postretirement Benefits [Member] \| U.S. Defined Benefit Plans [Member]
Change in Benefit Obligations:
Benefit obligation at beginning of year	29	33
Interest cost	1	1	1
(Gain) Loss from changes in actuarial assumptions and plan experience	1	(2)
Benefits paid	(3)	(3)
Benefit obligation at end of year	28	29	33
Change in Plan Assets:
Employer contribution	3	3
Benefits paid	(3)	(3)
Funded status	(28)	(29)
Recognized asset (liability)	(28)	(29)
Postretirement Benefits [Member] \| Foreign Plans [Member]
Change in Benefit Obligations:
Benefit obligation at beginning of year	19	20
Interest cost	1	1	1
Foreign currency exchange rate changes	(1)	(1)
(Gain) Loss from changes in actuarial assumptions and plan experience	2
Benefits paid	(1)	(1)
Benefit obligation at end of year	20	19	$ 20
Change in Plan Assets:
Employer contribution	1	1
Benefits paid	(1)	(1)
Funded status	(20)	(19)
Recognized asset (liability)	$ (20)	$ (19)

Employee Benefit Plans - Assumptions Used to Determine Pension Benefit Obligations and Periodic Benefit Costs, Postretirement Benefit Obligations and Net Costs (Detail)	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Pension Benefits [Member] \| U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.60%	4.20%	3.60%
Discount rate - benefit obligation	4.20%	3.60%	3.40%
Discount rate - interest cost	3.90%	3.00%	2.70%
Expected long-term rate of return on plan assets	6.30%	6.80%	6.80%
Pension Benefits [Member] \| Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	1.80%	2.40%	2.40%
Initial health care cost trend rate	3.00%	2.70%	2.70%
Discount rate - benefit obligation	2.40%	2.40%	1.80%
Discount rate - service cost	2.50%	2.40%	1.80%
Discount rate - interest cost	2.10%	2.00%	1.50%
Expected long-term rate of return on plan assets	4.90%	4.90%	4.70%
Initial health care cost trend rate	2.70%	2.70%	2.80%
Postretirement Benefits [Member] \| U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.90%	4.10%	3.40%
Initial health care cost trend rate	6.50%	7.00%	7.00%
Discount rate - benefit obligation	4.10%	3.40%	3.00%
Discount rate - service cost	4.00%	3.10%	2.60%
Discount rate - interest cost	3.70%	2.80%	2.40%
Initial health care cost trend rate	7.00%	7.00%	7.00%
Postretirement Benefits [Member] \| Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.40%	3.20%	3.10%
Initial health care cost trend rate	6.90%	7.00%	7.10%
Discount rate - benefit obligation	3.20%	3.10%	2.80%
Discount rate - service cost	3.50%	3.60%	3.20%
Discount rate - interest cost	3.10%	3.00%	2.60%
Initial health care cost trend rate	7.00%	7.10%	6.10%

Employee Benefit Plans - Amounts Recognized in Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Noncurrent liabilities	$ (91)	$ (118)
Pension Benefits [Member] \| U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets		10
Current liabilities	(3)
Noncurrent liabilities	(3)	(4)
Pension Benefits [Member] \| Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Noncurrent assets	19	21
Current liabilities	(1)	(1)
Noncurrent liabilities	(43)	(70)
Postretirement Benefits [Member] \| U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Current liabilities	(3)	(3)
Noncurrent liabilities	(25)	(26)
Postretirement Benefits [Member] \| Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Current liabilities		(1)
Noncurrent liabilities	$ (20)	$ (18)

Employee Benefit Plans - Amounts Recognized in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	$ (7)
Pension Benefits [Member] \| U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	13	$ (1)
Balance in accumulated other comprehensive income (loss), pretax	13	(1)
Pension Benefits [Member] \| Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	36	49
Net prior service credit		(1)
Balance in accumulated other comprehensive income (loss), pretax	36	48
Postretirement Benefits [Member] \| U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	(6)	(7)
Net prior service credit		(2)
Balance in accumulated other comprehensive income (loss), pretax	(6)	(9)
Postretirement Benefits [Member] \| Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	6	4
Balance in accumulated other comprehensive income (loss), pretax	$ 6	$ 4

Employee Benefit Plans - Estimated Future Benefit Payments (Detail)
$ in Millions

Sep. 30, 2019

USD ($)

Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]

Defined Benefit Plan Disclosure [Line Items]

2020

$ 158

^[1]

2025 - 2029

Pension Benefits [Member] | Foreign Plans [Member]

Defined Benefit Plan Disclosure [Line Items]

^[1]

Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]

Defined Benefit Plan Disclosure [Line Items]

^[1]

Postretirement Benefits [Member] | Foreign Plans [Member]

Defined Benefit Plan Disclosure [Line Items]

^[1]

$ 4

[1]	^{The $158 million expected payment for U.S. pension benefits in fiscal 2020 is in connection with the termination of the U.S. plan which is expected to be completed in fiscal 2020.}

Employee Benefit Plans - Estimated Future Benefit Payments (Parenthetical) (Detail)
$ in Millions

Sep. 30, 2019

USD ($)

Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]

Defined Benefit Plan Disclosure [Line Items]

Defined benefit plan expected payment

$ 158

^[1]

[1]	^{The $158 million expected payment for U.S. pension benefits in fiscal 2020 is in connection with the termination of the U.S. plan which is expected to be completed in fiscal 2020.}

Employee Benefit Plans - Net Periodic Defined Benefit Pension and Other Postretirement Benefit Costs (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Pension Benefits [Member] \| U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1	$ 1
Interest cost	5	5	4
Expected return on plan assets	(9)	(10)	(9)
Net periodic (benefit) cost	(3)	(4)	(4)
Pension Benefits [Member] \| Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	9	10
Interest cost	5	7	6
Expected return on plan assets	(10)	(15)	(14)
Amortization of prior service cost	2
Net losses	2	3	5
Settlements or Curtailments cost	(7)
Net periodic (benefit) cost	(1)	4	7
Postretirement Benefits [Member] \| U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1	1
Amortization of prior service cost	(2)	(3)	(3)
Net losses	(1)	(1)
Net periodic (benefit) cost	(2)	(3)	(2)
Postretirement Benefits [Member] \| Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1	1
Net periodic (benefit) cost	$ 1	$ 1	$ 1

Employee Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss), Pre-Tax (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Gain on settlements	$ 13
Pension Benefits [Member] \| U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		$ 14	$ (4)	$ (9)
Net changes recognized in Total other comprehensive (income) loss		14	(4)	(9)
Pension Benefits [Member] \| Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		(16)		(35)
Prior service (credit) cost		3
Amortization of prior service credit		(2)
Amortization of prior unrecognized loss		(2)	(3)	(5)
Loss on divestiture		(2)
Gain on settlements		7
Net changes recognized in Total other comprehensive (income) loss		(12)	(3)	(40)
Postretirement Benefits [Member] \| U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses			(2)	(3)
Amortization of prior service credit		2	3	3
Amortization of prior unrecognized loss		1	1
Net changes recognized in Total other comprehensive (income) loss		3	2
Postretirement Benefits [Member] \| Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		2	(1)	(1)
Net changes recognized in Total other comprehensive (income) loss		$ 2	$ (1)	$ (1)

Employee Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss), Pre-Tax (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Compensation And Retirement Disclosure [Abstract]
Other Comprehensive (Income) Loss, pension and other postretirement tax benefit (provision)	$ 5	$ (1)	$ (7)

Employee Benefit Plans - Defined Benefit Pension Plans Weighted-Average Asset Allocations (Detail)	Sep. 30, 2019	Sep. 30, 2018
U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity securities		40.00%
Debt securities	68.00%	60.00%
Cash and other securities	32.00%
Total	100.00%	100.00%
Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity securities	39.00%	39.00%
Debt securities	50.00%	53.00%
Cash and other securities	11.00%	8.00%
Total	100.00%	100.00%

Stock-Based Compensation - Additional Information (Detail) - USD ($)

12 Months Ended

Sep. 30, 2019

Sep. 30, 2018

Sep. 30, 2017

Mar. 09, 2017

Mar. 08, 2012

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Percentage of vesting in first anniversary

30.00%

Percentage of vesting in second anniversary

30.00%

Percentage of vesting in third anniversary

40.00%

Net stock-based compensation expense

$ 8,000,000

$ 16,000,000

$ 10,000,000

(Provision) benefit for income taxes

$ 70,000,000

193,000,000

33,000,000

Stock Options, Weighted Average Grant Date Fair Value, Granted

$ 10.85

Stock Options [Member]

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Percentage of exercise price equal to market price on the date of grant

100.00%

Vesting period (in years)

3 years

Expiration period, years

10 years

Unrecognized compensation cost

$ 2,000,000

Weighted-average period, years

1 year

Options outstanding, aggregate intrinsic value

$ 0

Options exercisable, aggregate intrinsic value

$ 0

Closing stock price

$ 45.32

Intrinsic value of options exercised

$ 1,000,000

11,000,000

16,000,000

Cash received from exercises

2,000,000

22,000,000

$ 21,000,000

(Provision) benefit for income taxes

$ 1,000,000

Stock Options, Weighted Average Grant Date Fair Value, Granted

$ 10.85

$ 15.21

$ 12.76

Restricted Stock Units [Member]

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Vesting period (in years)

3 years

Unrecognized compensation cost

$ 16,000,000

Weighted-average period, years

1 year

Estimated weighted average grant date fair value

$ 49.44

^[1]

$ 62.18

$ 51.03

Intrinsic value of restricted stock units vested

$ 18,000,000

$ 12,000,000

$ 7,000,000

Restricted Stock [Member]

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Vesting period (in years)

3 years

2009 Long-Term Incentive Plan [Member] | Maximum [Member]

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Common stock, authorized shares

8,854,000

2017 Long-Term Incentive Plan [Member] | Maximum [Member]

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Common stock, authorized shares

5,375,000

Supplemental 401(k) Plan [Member]

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Supplemental retirement savings plan, aggregate value of the accounts, shares

93,000

116,000

Supplemental retirement savings plan aggregate value of the accounts paid in cash

$ 1,000,000

[1]	The number granted represents the number of shares issuable upon vesting of time-based restricted stock units and performance-based restricted stock units, assuming the Company performs at the target performance level in each year of the three-year performance period.

Stock-Based Compensation - Stock-Based Compensation Expenses (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense before tax	$ 11	$ 22	$ 16
Income tax benefit	(3)	(6)	(6)
Net stock-based compensation expense	8	16	10
Cost of Sales [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense before tax	1	2	1
Selling and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense before tax	9	19	14
Research and Technical Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense before tax	$ 1	$ 1	$ 1

Stock-Based Compensation - Equity Incentive Plan Activity (Detail) - $ / shares
shares in Thousands

12 Months Ended

Sep. 30, 2019

Sep. 30, 2018

Sep. 30, 2017

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Stock Options, Total Options, Outstanding at September 30, 2018

^[1]

881

Stock Options, Total Options, Granted

^[1]

343

Stock Options, Total Options, Exercised / Vested

^[1]

(49)

Stock Options, Total Options, Cancelled / Forfeited

^[1]

(153)

Stock Options, Total Options, Outstanding at September 30, 2019

^[1]

1,022

^[2]

881

Stock Options, Total Options, Exercisable at September 30, 2019

^[1]

499

Stock Options, Weighted Average Exercise Price, Outstanding at September 30, 2018

$ 50.73

Stock Options, Weighted Average Exercise Price, Granted

49.70

Stock Options, Weighted Average Exercise Price, Exercised / Vested

35.06

Stock Options, Weighted Average Exercise Price, Cancelled / Forfeited

54.44

Stock Options, Weighted Average Exercise Price, Outstanding at September 30, 2019

50.57

^[2]

$ 50.73

Stock Options, Weighted Average Exercise Price, Exercisable at September 30, 2019

48.09

Stock Options, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2018

13.82

Stock Options, Weighted Average Grant Date Fair Value, Granted

10.85

Stock Options, Weighted Average Grant Date Fair Value, Exercised / Vested

9.41

Stock Options, Weighted Average Grant Date Fair Value, Cancelled / Forfeited

10.36

Stock Options, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2019

$ 12.13

^[2]

$ 13.82

Restricted Stock Units [Member]

Share Based Compensation Arrangement By Share Based Payment Award [Line Items]

Restricted Stock / Units, Outstanding at September 30, 2018

^[3]

985

Restricted Stock / Units, Granted

^[3]

316

Restricted Stock / Units, Performance-based adjustment

^[3],[4]

Restricted Stock / Units, Exercised / Vested

^[3]

(383)

Restricted Stock / Units, Cancelled / Forfeited

^[3]

(163)

Restricted Stock / Units, Outstanding at September 30, 2019

^[3]

765

^[2]

985

Restricted Stock / Units, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2018

^[3]

$ 50.16

Restricted Stock / Units, Weighted Average Grant Date Fair Value, Granted

49.44

^[3]

$ 62.18

$ 51.03

Restricted Stock / Units, Weighted Average Grant Date Fair Value, Performance-based adjustment

^[3],[4]

62.98

Restricted Stock / Units, Weighted Average Grant Date Fair Value, Exercised / Vested

^[3]

40.97

Restricted Stock / Units, Weighted Average Grant Date Fair Value, Cancelled / Forfeited

^[3]

54.48

Restricted Stock / Units, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2019

^[3]

$ 53.71

^[2]

$ 50.16

[1]	Unvested stock options were approximately 523,000 and 546,000 at September 30, 2019 and 2018 and their weighted average grant date fair values were $52.95 and $54.48, respectively.
[2]	Stock options outstanding include options vested and expected to vest in the future and have a weighted average remaining contractual life of 6.74 years.
[3]	The number granted represents the number of shares issuable upon vesting of time-based restricted stock units and performance-based restricted stock units, assuming the Company performs at the target performance level in each year of the three-year performance period.
[4]	Represents the net incremental number of shares issuable upon vesting of performance-based restricted stock units based upon the achievement of the annual financial performance metrics for fiscal 2019.

Stock-Based Compensation - Equity Incentive Plan Activity (Parenthetical) (Detail) - $ / shares shares in Thousands	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock options outstanding include options vested and expected to vest in the future, weighted average remaining contractual life, in years	6 years 8 months 26 days
Unvested stock options	523,000	546,000
Unvested stock options, weighted average grant date fair value	$ 52.95	$ 54.48

Stock-Based Compensation - Weighted-Average Assumptions (Detail) - $ / shares	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected stock price volatility	27.00%	28.00%	32.00%
Risk free interest rate	3.10%	2.20%	1.80%
Expected life of options (years)	6 years	6 years	6 years
Expected annual dividends per year	$ 1.32	$ 1.26	$ 1.20

Restructuring - Recorded Restructuring Activities (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Restructuring Cost And Reserve [Line Items]
Restructuring reserve, period expense	$ 16	$ (30)	$ 3
Cost of Sales [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring reserve, period expense	9	(31)	2
Selling and Administrative Expenses [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring reserve, period expense	$ 7	$ 1	$ 1

Restructuring - Restructuring Activities and Related Reserves (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Restructuring Cost And Reserve [Line Items]
Reserve balance	$ 5	$ 3	$ 5
Charges (gain)	16	(30)	3
Costs charged against assets (liabilities)	(2)	(2)	1
Cash (paid) received	(12)	34	(6)
Reserve balance	7	5	3
Severance and Employee Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	1	1	3
Charges (gain)	11	2	1
Cash (paid) received	(9)	(2)	(3)
Reserve balance	3	1	1
Environmental Remediation and Decommissioning Activities [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	4	2	2
Charges (gain)		3	1
Cash (paid) received		(1)	(1)
Reserve balance	4	4	2
Non-Cash Asset Impairment and Accelerated Depreciation [Member]
Restructuring Cost And Reserve [Line Items]
Charges (gain)	2	1
Costs charged against assets (liabilities)	(2)	(1)
Asset Sales [Member]
Restructuring Cost And Reserve [Line Items]
Charges (gain)		(38)
Costs charged against assets (liabilities)		(1)
Cash (paid) received		39
Other [Member]
Restructuring Cost And Reserve [Line Items]
Charges (gain)	3	2	1
Costs charged against assets (liabilities)			1
Cash (paid) received	$ (3)	$ (2)	$ (2)

Restructuring - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended				12 Months Ended
	Sep. 30, 2014	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2015	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Restructuring Cost And Reserve [Line Items]
Proceeds from the sale of land								$ 39
Purification Solutions Transformation Plan [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring Charges							$ 9
Professional fees and other charges							1
Restructuring cash payments of fiscal year							8
Accrued severance charges							1
Purification Solutions Transformation Plan [Member] \| Maximum [Member]
Restructuring Cost And Reserve [Line Items]
Severance costs							$ 8
Purification Solutions Transformation Plan [Member] \| Scenario, Forecast [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges expected in fiscal year						$ 1
Restructuring cash payments in fiscal 2020						$ 2
Operational Restructuring [Member] \| Thane, India [Member]
Restructuring Cost And Reserve [Line Items]
Proceeds from the sale of land		$ 28						28
Net benefit to earnings								$ 28
Refundable cash deposit	$ 22		$ 3		$ 3
Operational Restructuring [Member] \| Merak, Indonesia [Member] \| Cost of Sales [Member]
Restructuring Cost And Reserve [Line Items]
Proceeds from the sale of land				$ 13
Net benefit to earnings				$ 11

Accumulated Other Comprehensive Income (Loss) - Changes in Each Component of AOCI, Net of Tax (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 1,279	$ 1,625	$ 1,389
Ending Balance	1,134	1,279	1,625
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(266)	(204)
Other comprehensive income (loss) before reclassifications	(69)	(64)
Amounts reclassified from AOCI	(9)	(2)
Less: Other comprehensive income (loss) attributable to noncontrolling interests	(6)	(4)
Ending Balance	(338)	(266)	(204)
Unrealized Gains on Investment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	1	2
Other comprehensive income (loss) before reclassifications		(1)
Ending Balance	1	1	2
Pension and Other Postretirement Benefit Liability Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(52)	(57)
Other comprehensive income (loss) before reclassifications	4	6
Amounts reclassified from AOCI	(6)	(1)
Ending Balance	(54)	(52)	(57)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(317)	(259)	(325)
Other comprehensive income (loss) before reclassifications	(65)	(59)
Amounts reclassified from AOCI	(15)	(3)	2
Less: Other comprehensive income (loss) attributable to noncontrolling interests	(6)	(4)
Ending Balance	$ (391)	$ (317)	$ (259)

Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified Out of AOCI (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
(Gains) Losses Reclassified to Interest Expense [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (5)	$ (5)
(Gains) Losses Excluded from Effectiveness Testing and Amortized to Interest Expense [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	1	2
Amortization of Actuarial Losses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	1	2	$ 5
Amortization of Prior Service Cost (Credit) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		(3)	(3)
Settlement and Curtailment Gain [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(7)
Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(13)	(4)	2
Tax impact	(2)	1
Total after tax	(15)	$ (3)	$ 2
Specialty Fluids Divestiture [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (3)

Earnings Per Share - Components of Basic and Diluted Earnings Per Common Share (EPS) (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Basic EPS:
Net income (loss) attributable to Cabot Corporation	$ 33	$ 32	$ 23	$ 69	$ 94	$ 88	$ (173)	$ (122)	$ 157	$ (113)	$ 248
Less: Dividends and dividend equivalents to participating securities									1	1
Less: Undistributed earnings allocated to participating securities									1		2
Earnings (loss) allocated to common shareholders (numerator)									$ 155	$ (114)	$ 246
Weighted average common shares and participating securities outstanding									59.5	62.4	62.8
Less: Participating securities									0.8	0.7	0.5
Adjusted weighted average common shares (denominator)									58.7	61.7	62.3
Basic	$ 0.56	$ 0.55	$ 0.39	$ 1.14	$ 1.51	$ 1.41	$ (2.80)	$ (1.98)	$ 2.64	$ (1.85)	$ 3.94
Diluted EPS:
Earnings (loss) allocated to common shareholders									$ 155	$ (114)	$ 246
Plus: Earnings (loss) allocated to participating securities									2		2
Less: Adjusted earnings allocated to participating securities									2		2
Earnings (loss) available to common shares (numerator)									$ 155	$ (114)	$ 246
Adjusted weighted average common shares outstanding									58.7	61.7	62.3
Common shares issuable									0.1		0.4
Adjusted weighted average common shares (denominator)									58.8	61.7	62.7
Diluted	$ 0.55	$ 0.55	$ 0.39	$ 1.14	$ 1.51	$ 1.40	$ (2.80)	$ (1.98)	$ 2.63	$ (1.85)	$ 3.91

Earnings Per Share - Calculation of Undistributed Earnings (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income (loss) attributable to Cabot Corporation	$ 33	$ 32	$ 23	$ 69	$ 94	$ 88	$ (173)	$ (122)	$ 157	$ (113)	$ 248
Less: Dividends declared on common stock									80	79	77
Less: Dividends and dividend equivalents to participating securities									1	1
Undistributed earnings (loss)									76	(193)	171
Undistributed earnings (loss) allocated to common shareholders									75	$ (193)	169
Undistributed earnings allocated to participating securities									$ 1		$ 2

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Earnings Per Share - Components of Basic and Diluted Earnings Per Common Share (Parenthetical) (Detail) - shares	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share	942,060	229,220	179,052

Income Taxes - Income Before Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments [Abstract]
Domestic	$ (66)	$ (229)	$ (8)
Foreign	321	346	307
Income (loss) from continuing operations before income taxes and equity in earnings of affiliated companies	$ 255	$ 117	$ 299

Income Taxes - Provision (Benefit) for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
U.S. federal and state, Current	$ 2	$ 14	$ 5
U.S. federal and state, Deferred	(30)	114	(26)
U.S. federal and state, Total	(28)	128	(21)
Foreign, Current	95	88	59
Foreign, Deferred	3	(23)	(5)
Foreign, Total	98	65	54
Provision (benefit) for income taxes	$ 70	$ 193	$ 33

Income Taxes - Reconciliation Using U.S. Statutory Rate (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Computed tax expense at the federal statutory rate	$ 53	$ 29	$ 105
Impact of taxation at different rates, repatriation, losses and other	42	6	(75)
Impact of increase (decrease) in valuation allowance on deferred taxes	(25)	(16)	(7)
Impact of foreign losses for which a current tax benefit is not available			1
Impact of non-deductible net currency losses		2
Impact of the Tax Cuts and Jobs Act of 2017		159
Global Intangible Low Taxed Income (GILTI)	10
U.S. and state benefits from research and experimentation activities	(2)	(2)	(2)
Provision (settlement) of unrecognized tax benefits	(8)	1	7
Impact of goodwill impairment charge		18
Permanent differences, net	1	(1)	5
State taxes, net of federal effect	(1)	(3)	(1)
Provision (benefit) for income taxes	$ 70	$ 193	$ 33

Income Taxes - Additional Information (Detail) - USD ($)		3 Months Ended		12 Months Ended
	Jan. 01, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Taxes [Line Items]
Net tax benefit related to unrecognized tax position				$ 4,000,000
Net tax benefit related to pension settlement				2,000,000
Net tax benefit related to specialty fluids sale				2,000,000
Net tax benefit related to result of changes in non-us tax laws				1,000,000
Net tax expense from impact of Tax Cuts and Job Act of 2017					$ 159,000,000
Net tax expense upon sale of assets					3,000,000
Net tax benefits related to impairment					29,000,000
Net discrete tax (benefits) charges related to tax settlements		$ 19,000,000		(7,000,000)	120,000,000	$ (25,000,000)
Net tax benefits from excess foreign tax credits upon repatriation of prior foreign earnings and accrual on certain foreign earnings						16,000,000
Net tax benefits from change in valuation allowance				2,000,000	15,000,000	6,000,000
Net tax (benefits) partially offset by charges for return to provision adjustments related to tax return filings and audit settlements				5,000,000		(4,000,000)
Other miscellaneous tax items				$ 1,000,000	2,000,000	1,000,000
Income tax rate	21.00%		35.00%
Percentage of dividend received deduction for foreign dividends				100.00%
BEAT liability				$ 0
Impact on earnings of increase in effective tax rate				$ 10,000,000
Percentage of pro rata share in CFC for determining GILTI requirements				10.00%
Net operating loss carryforwards				$ 711,000,000
Other tax credit carryforwards				99,000,000
Undistributed earnings				1,316,000,000
Foreign tax credit carry forwards		12,000,000		20,000,000	12,000,000
Required future taxable operating income				$ 606,000,000
Expected term to realize deferred tax asset, years				20 years
Increased/(decreased) valuation allowance				$ (45,000,000)	1,000,000
Unrecognized tax benefits		37,000,000		27,000,000	37,000,000	36,000,000	$ 30,000,000
Unrecognized tax benefits, recorded				17,000,000
Unrecognized tax benefits, not recorded				10,000,000
Accruals for penalties		1,000,000			1,000,000
Accruals for interest		$ 9,000,000		7,000,000	9,000,000
Total penalties and interest				2,000,000	$ 2,000,000	$ 2,000,000
Favorable impact on tax provision				$ 27,000,000
Earliest Tax Year [Member] \| State Tax Authorities [Member]
Income Taxes [Line Items]
Tax years remain subject to examination				2005
Earliest Tax Year [Member] \| Non-U.S. Jurisdictions [Member]
Income Taxes [Line Items]
Tax years remain subject to examination				2003
Earliest Tax Year [Member] \| United States Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Tax years remain subject to examination				2016
Latest Tax Year [Member] \| State Tax Authorities [Member]
Income Taxes [Line Items]
Tax years remain subject to examination				2018
Latest Tax Year [Member] \| Non-U.S. Jurisdictions [Member]
Income Taxes [Line Items]
Tax years remain subject to examination				2018
Latest Tax Year [Member] \| United States Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Tax years remain subject to examination				2018
Specialty Fluids [Member]
Income Taxes [Line Items]
Operating losses subject to expiration				$ 16,000,000
U.S. Defined Benefit Plans [Member]
Income Taxes [Line Items]
Net deferred tax assets				127,000,000
Foreign tax credit carry forwards				$ 20,000,000
Maximum [Member]
Income Taxes [Line Items]
Base erosion percentage				3.00%
Accruals for penalties				$ 1,000,000

Income Taxes - Components of Deferred Income Taxes (Detail) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018
Components Of Deferred Tax Assets [Abstract]
Deferred expenses	$ 15	$ 17
Intangible assets	28	23
Inventory	9	4
Other	3	4
Pension and other benefits	41	45
Net operating loss carryforwards	124	146
Foreign tax credit carryforwards	20	12
R&D credit carryforwards	43	41
Other business credit carryforwards	29	39
Subtotal	312	331
Valuation allowance	(124)	(169)
Total deferred tax assets	188	162
Property, plant and equipment	(61)	(56)
Unremitted earnings of non-U.S. subsidiaries	(5)	(14)
Total deferred tax liabilities	$ (66)	$ (70)

Income Taxes - Expiration Dates of Carryforwards (Detail) $ in Millions	Sep. 30, 2019 USD ($)
Significant Tax Attributes And Dates Of Expiration [Line Items]
Net operating loss carryforwards	$ 711
Credits	99
2020 - 2026 [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
Net operating loss carryforwards	262
Credits	40
2027 and thereafter [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
Net operating loss carryforwards	168
Credits	57
Indefinite Carryforwards [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
Net operating loss carryforwards	281
Credits	$ 2

Income Taxes - Expiration Dates of Carryforwards (Parenthetical) (Detail)	12 Months Ended
	Sep. 30, 2019
Significant Tax Attributes And Dates Of Expiration [Line Items]
Expiration periods	2027
Minimum [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
Expiration periods	2020
Maximum [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
Expiration periods	2026

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Balance at beginning of the year	$ 37	$ 36	$ 30
Additions based on tax provisions related to the current year		2	2
Additions for tax positions of prior years		1	8
Reductions of tax provisions of prior years	(1)		(1)
Reductions related to settlements	(5)		(2)
Reductions from lapse of statute of limitations	(4)	(2)	(1)
Balance at end of the year	$ 27	$ 37	$ 36

Commitments and Contingencies - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) claimants	Sep. 30, 2019 USD ($) claimants	Sep. 30, 2018 USD ($) claimants	Sep. 30, 2017 USD ($)
Loss Contingencies [Line Items]
Lease expiration period, years		10 years
Rent expense under such operating lease agreement		$ 27,000,000	$ 32,000,000	$ 33,000,000
Raw material purchased		466,000,000	441,000,000	331,000,000
Long term purchase commitment related to information technology		$ 12,000,000
Purchase agreement period		5 years
Charges for environmental expense			$ 6,000,000
Respirator Liabilities [Member]
Loss Contingencies [Line Items]
Annual fees paid by transferee to transferor company		$ 400,000
Number of claimants \| claimants	35,000	35,000	35,000
Respirator reserve	$ 35,000,000	$ 35,000,000	$ 25,000,000
Respirator charge	20,000,000
Cash payments for respirator reserves		10,000,000	3,000,000	3,000,000
Respirator Liabilities [Member] \| Selling and Administrative Expenses [Member]
Loss Contingencies [Line Items]
Respirator charge		20,000,000	10,000,000	0
Environmental Matters [Member]
Loss Contingencies [Line Items]
Reserved for environmental matters	13,000,000	13,000,000	15,000,000
Reserve for environmental matters included in accrued expenses	9,000,000	9,000,000	12,000,000
Reserve for environmental matters included in other liabilities	4,000,000	4,000,000	3,000,000
Cash payments for environmental reserves		2,000,000	3,000,000	2,000,000
Environmental Matters [Member] \| Operating and Maintenance Component [Member]
Loss Contingencies [Line Items]
Reserved for environmental matters	4,000,000	4,000,000
Per Accident for Auto [Member]
Loss Contingencies [Line Items]
Self-insured liability	500,000	500,000
Per Occurrence for All Other [Member]
Loss Contingencies [Line Items]
Self-insured liability	2,000,000	2,000,000
Per Accident for U.S. Workers' Compensation [Member]
Loss Contingencies [Line Items]
Self-insured liability	1,000,000	1,000,000
Maximum [Member]
Loss Contingencies [Line Items]
Retention for medical costs per person per annum	250,000	250,000
Charges for environmental expense		$ 1,000,000		1,000,000
Minimum [Member] \| Respirator Liabilities [Member]
Loss Contingencies [Line Items]
Periods of pending claim		10 years
Non-Controlling Interests [Member]
Loss Contingencies [Line Items]
Raw material purchased		$ 156,000,000	156,000,000	$ 116,000,000
Accounts payable and accrued liabilities	$ 20,000,000	$ 20,000,000	$ 8,000,000

Commitments and Contingencies - Schedule of Future Minimum Rental Commitments under Non-Cancelable Leases (Detail) $ in Millions	Sep. 30, 2019 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2020	$ 23
2021	14
2022	9
2023	9
2024	8
2025 and thereafter	68
Total future minimum rental commitments	$ 131

Commitments and Contingencies - Schedule of Raw Material Purchased under Long Term Purchase Agreements (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	$ 466	$ 441	$ 331
Reinforcement Materials [Member]
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	393	375	281
Performance Chemicals [Member]
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	65	55	43
Purification Solutions [Member]
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	$ 8	$ 11	$ 7

Commitments and Contingencies - Schedule of Components of Purchase Commitments (Detail) $ in Millions	Sep. 30, 2019 USD ($)
Long-term Purchase Commitment [Line Items]
Payments Due by Fiscal Year 2020	$ 281
Payments Due by Fiscal Year 2021	179
Payments Due by Fiscal Year 2022	169
Payments Due by Fiscal Year 2023	143
Payments Due by Fiscal Year 2024	137
Payments Due Thereafter	1,648
Payments Due, Total	2,557
Reinforcement Materials [Member]
Long-term Purchase Commitment [Line Items]
Payments Due by Fiscal Year 2020	218
Payments Due by Fiscal Year 2021	123
Payments Due by Fiscal Year 2022	116
Payments Due by Fiscal Year 2023	108
Payments Due by Fiscal Year 2024	107
Payments Due Thereafter	1,246
Payments Due, Total	1,918
Performance Chemicals [Member]
Long-term Purchase Commitment [Line Items]
Payments Due by Fiscal Year 2020	57
Payments Due by Fiscal Year 2021	55
Payments Due by Fiscal Year 2022	53
Payments Due by Fiscal Year 2023	35
Payments Due by Fiscal Year 2024	30
Payments Due Thereafter	402
Payments Due, Total	632
Purification Solutions [Member]
Long-term Purchase Commitment [Line Items]
Payments Due by Fiscal Year 2020	6
Payments Due by Fiscal Year 2021	1
Payments Due, Total	$ 7

Financial Information by Segment & Geographic Area - Additional Information (Detail)		9 Months Ended	12 Months Ended
	Jun. 28, 2019 Segment	Jun. 28, 2019 Segment	Sep. 30, 2019 Segment Business_Unit
Segment Reporting Information [Line Items]
Number of business reportable segments	3	4
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Number of business reportable segments			1
Number of business activity \| Business_Unit			2

Financial Information by Segment & Geographic Area - Schedule of Performance Segment (Detail) - Performance Chemicals [Member] - Operating Segments [Member] - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Net sales	$ 995	$ 1,028	$ 908
Performance Additives [Member]
Segment Reporting Information [Line Items]
Net sales	694	707	650
Formulated Solutions [Member]
Segment Reporting Information [Line Items]
Net sales	$ 301	$ 321	$ 258

Financial Information by Segment & Geographic Area - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues from external customers	$ 827	$ 845	$ 844	$ 821	$ 850	$ 854	$ 818	$ 720	$ 3,337	$ 3,242	$ 2,717
Depreciation and amortization									148	149	155
Equity in earnings of affiliated companies									1	2	7
Income (loss) from continuing operations before income taxes									255	117	299
Assets	3,004				3,244				3,004	3,244	3,338
Total expenditures for additions to long-lived assets									247	229	147
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									3,144	3,126	2,611
Depreciation and amortization									147	152	156
Equity in earnings of affiliated companies									3	7	12
Income (loss) from continuing operations before income taxes									444	480	409
Assets	2,637				2,876				2,637	2,876	2,778
Total expenditures for additions to long-lived assets									242	224	139
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									193	116	106
Depreciation and amortization									1	(3)	(1)
Equity in earnings of affiliated companies									(2)	(5)	(5)
Income (loss) from continuing operations before income taxes									(189)	(363)	(110)
Assets	367				368				367	368	560
Total expenditures for additions to long-lived assets									5	5	8
Reinforcement Materials [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									1,815	1,774	1,381
Depreciation and amortization									69	70	69
Equity in earnings of affiliated companies									(1)	1	6
Income (loss) from continuing operations before income taxes									266	279	193
Assets	1,177				1,319				1,177	1,319	1,189
Total expenditures for additions to long-lived assets									82	97	68
Performance Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									995	1,028	908
Depreciation and amortization									51	48	46
Equity in earnings of affiliated companies									1
Income (loss) from continuing operations before income taxes									152	200	201
Assets	1,024				919				1,024	919	708
Total expenditures for additions to long-lived assets									148	94	47
Purification Solutions [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									278	279	281
Depreciation and amortization									26	32	39
Equity in earnings of affiliated companies									3	6	6
Income (loss) from continuing operations before income taxes									2	(7)	6
Assets	$ 436				460				436	460	741
Total expenditures for additions to long-lived assets									11	16	19
Specialty Fluids [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									56	45	41
Depreciation and amortization									1	2	2
Income (loss) from continuing operations before income taxes									24	8	9
Assets					$ 178					178	140
Total expenditures for additions to long-lived assets									$ 1	$ 17	$ 5

Financial Information by Segment & Geographic Area - Financial Information by Reportable Segment (Parenthetical) (Detail)	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting [Abstract]
Percentage of sale of an equity method affiliate	100.00%	100.00%	100.00%

Financial Information by Segment & Geographic Area - Sales of Equity Method Affiliate and Discounting Charges for Certain Notes Receivable (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues from external customers	$ 827	$ 845	$ 844	$ 821	$ 850	$ 854	$ 818	$ 720	$ 3,337	$ 3,242	$ 2,717
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									193	116	106
Unallocated and Other [Member] \| Royalties, the Impact of Unearned Revenue, the Removal of 100% of the Sales of an Equity Method Affiliate and Discounting Charges for Certain Notes Receivable [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									(13)	11	11
Unallocated and Other [Member] \| Shipping and Handling Costs [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									130	$ 105	$ 95
Unallocated and Other [Member] \| By-product Sales [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									$ 76

Financial Information by Segment & Geographic Area - Sales of Equity Method Affiliate and Discounting Charges for Certain Notes Receivable (Parenthetical) (Detail)	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting [Abstract]
Percentage of sale of an equity method affiliate	100.00%	100.00%	100.00%

Financial Information by Segment & Geographic Area - Schedule of Income (Loss) from Continuing Operations before Income Taxes and Equity in Earnings of Affiliated Companies for Unallocated and Other (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Interest expense		$ (59)	$ (54)	$ (53)
Global restructuring activities		(16)	30	(3)
Goodwill and long-lived assets impairment charge		(29)
Gains (losses) on sale of investments			10
Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Loss on sale and asset impairment charge		(29)
Purification Solutions [Member]
Segment Reporting Information [Line Items]
Goodwill and long-lived assets impairment charge	$ (224)
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Interest expense		(59)	(54)	(53)
Unallocated corporate costs		(50)	(61)	(50)
General unallocated income (expense)		8	2	3
Less: Equity in earnings of affiliated companies, net of tax		1	2	7
Income from continuing operations before income taxes and equity in earnings of affiliated companies		(189)	(363)	(110)
Certain Items [Member]
Segment Reporting Information [Line Items]
Legal and environmental matters and reserves		(21)	(16)	1
Global restructuring activities		(16)	30	(3)
Acquisition and integration-related charges		(6)	(2)
Executive transition costs		(1)	(2)
Inventory reserve adjustment			(13)
Gains (losses) on sale of investments			10
Other certain items		(3)	(1)	(1)
Total certain items, pre-tax		(87)	(248)	$ (3)
Certain Items [Member] \| Equity Affiliate Investment [Member]
Segment Reporting Information [Line Items]
Investment impairment charge		$ (11)
Certain Items [Member] \| Purification Solutions [Member]
Segment Reporting Information [Line Items]
Goodwill and long-lived assets impairment charge			$ (254)

Financial Information by Segment & Geographic Area - Revenue from External Customers and Long-Lived Asset Information by Geographic Area (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues from external customers	$ 827	$ 845	$ 844	$ 821	$ 850	$ 854	$ 818	$ 720	$ 3,337	$ 3,242	$ 2,717
Net property, plant and equipment	1,348				1,296				1,348	1,296	1,305
United States [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues from external customers									702	676	645
Net property, plant and equipment	572				493				572	493	493
China [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues from external customers									738	752	573
Net property, plant and equipment	264				270				264	270	261
Other Countries [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues from external customers									1,897	1,814	1,499
Net property, plant and equipment	$ 512				$ 533				$ 512	$ 533	$ 551

Financial Information by Segment & Geographic Area - Revenue from External Customers by Geographic Region (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 827	$ 845	$ 844	$ 821	$ 850	$ 854	$ 818	$ 720	$ 3,337	$ 3,242	$ 2,717
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									3,144	3,126	2,611
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									193	116	106
Reinforcement Materials [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									1,815	1,774	1,381
Performance Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									995	1,028	908
Purification Solutions [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									278	279	281
Specialty Fluids [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									56	$ 45	$ 41
Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									1,114
Americas [Member] \| Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									688
Americas [Member] \| Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									294
Americas [Member] \| Purification Solutions [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									126
Americas [Member] \| Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									6
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									1,158
Asia Pacific [Member] \| Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									769
Asia Pacific [Member] \| Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									353
Asia Pacific [Member] \| Purification Solutions [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									35
Asia Pacific [Member] \| Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									1
Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									872
Europe, Middle East and Africa [Member] \| Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									358
Europe, Middle East and Africa [Member] \| Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									348
Europe, Middle East and Africa [Member] \| Purification Solutions [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									117
Europe, Middle East and Africa [Member] \| Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									$ 49

Unaudited Quarterly Financial Information - Schedule of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Quarterly Financial Information Disclosure [Abstract]
Net sales and other operating revenues	$ 827	$ 845	$ 844	$ 821	$ 850	$ 854	$ 818	$ 720	$ 3,337	$ 3,242	$ 2,717
Gross profit	171	170	178	166	211	197	188	176	685	772	657
Net income (loss)	40	40	29	77	102	99	(163)	(112)	186	(74)	273
Net income (loss) attributable to Cabot Corporation	$ 33	$ 32	$ 23	$ 69	$ 94	$ 88	$ (173)	$ (122)	$ 157	$ (113)	$ 248
Earnings per common share—basic	$ 0.56	$ 0.55	$ 0.39	$ 1.14	$ 1.51	$ 1.41	$ (2.80)	$ (1.98)	$ 2.64	$ (1.85)	$ 3.94
Earnings per common share—diluted	$ 0.55	$ 0.55	$ 0.39	$ 1.14	$ 1.51	$ 1.40	$ (2.80)	$ (1.98)	$ 2.63	$ (1.85)	$ 3.91

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

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- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

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- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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- Definition

The consolidated profit or loss for the period, net of income taxes, including the portion attributable to the noncontrolling interest.

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+ Details

Unaudited Quarterly Financial Information - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Schedule Of Quarterly Financial Information Disclosure [Line Items]
Proceeds from the sale of land				$ 39
Net discrete tax (benefits) charges related to tax settlements		$ 19	$ (7)	120	$ (25)
Operational Restructuring [Member] \| Thane, India [Member]
Schedule Of Quarterly Financial Information Disclosure [Line Items]
Proceeds from the sale of land		$ 28		$ 28
Respirator Liabilities [Member]
Schedule Of Quarterly Financial Information Disclosure [Line Items]
Respirator charge	$ 20