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Document and Entity Information - shares	9 Months Ended
Document and Entity Information - shares	Jun. 30, 2015	Aug. 04, 2015
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q3
Trading Symbol	CBT
Entity Registrant Name	CABOT CORP
Entity Central Index Key	0000016040
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		62,914,994

Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement [Abstract]
Net sales and other operating revenues	$ 694	$ 940	$ 2,200	$ 2,736
Cost of sales	544	756	1,754	2,197
Gross profit	150	184	446	539
Selling and administrative expenses	67	76	216	245
Research and technical expenses	15	15	44	46
Income from operations	68	93	186	248
Interest and dividend income	1	1	3	3
Interest expense	(13)	(14)	(40)	(41)
Other (expense) income	(3)		(6)	27
Long-lived assets impairment charge (Note F)	(209)		(209)	(4)
Goodwill impairment charge (Note F)	(353)		(353)
(Loss) income from continuing operations	(509)	80	(419)	237
Benefit (provision) for income taxes	64	(20)	47	(51)
Equity in earnings (loss) of affiliated companies, net of tax	1	(2)	4	(2)
(Loss) income from continuing operations	(444)	58	(368)	184
Income (loss) from discontinued operations, net of tax	1	(1)	1	(2)
Net (loss) income	(443)	57	(367)	182
Net income attributable to noncontrolling interests, net of tax	2	5	7	14
Net (loss) income attributable to Cabot Corporation	$ (445)	$ 52	$ (374)	$ 168
Weighted-average common shares outstanding, in millions:
Basic	63.3	64.5	63.7	64.3
Diluted	63.3	65.2	63.7	65.0
Basic:
(Loss) income from continuing operations attributable to Cabot Corporation	$ (7.05)	$ 0.80	$ (5.89)	$ 2.61
Income (loss) from discontinued operations	0.01	(0.01)	0.01	(0.03)
Net (loss) income attributable to Cabot Corporation	(7.04)	0.79	(5.88)	2.58
Diluted:
(Loss) income from continuing operations attributable to Cabot Corporation	(7.05)	0.79	(5.89)	2.58
Income (loss) from discontinued operations	0.01	(0.01)	0.01	(0.03)
Net (loss) income attributable to Cabot Corporation	(7.04)	0.78	(5.88)	2.55
Dividends per common share	$ 0.22	$ 0.22	$ 0.66	$ 0.62

Consolidated Statements of Comprehensive (Loss) Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Net (loss) income	$ (443)	$ 57	$ (367)	$ 182
Other comprehensive income (loss), net of tax
Foreign currency translation adjustment (net of tax provision of $-, $-, $1 and $1)	18	11	(216)	(18)
Unrealized holding gains arising during the period (net of tax provision of $-, $1, $- and $-)		2		2
Pension and other postretirement benefit liability adjustments
Pension and other postretirement benefit liability adjustments arising during the period (net of tax provision of $-, $-, $6 and $-)			21
Amortization of net loss and prior service credit included in net periodic pension cost (net of tax benefit of less than $1 million in all periods)			1	1
Other comprehensive income (loss)	18	13	(194)	(15)
Comprehensive (loss) income	(425)	70	(561)	167
Net income attributable to noncontrolling interests	2	5	7	14
Noncontrolling interests foreign currency translation adjustment, net of tax			(3)	(2)
Comprehensive income attributable to noncontrolling interests, net of tax	2	5	4	12
Comprehensive (loss) income attributable to Cabot Corporation	$ (427)	$ 65	$ (565)	$ 155

Consolidated Statements of Comprehensive (Loss) Income (Parenthetical) (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Foreign currency translation adjustment, tax provision (benefit)			$ 1	$ 1
Unrealized holding gains (losses) arising during the period, tax provision		$ 1
Pension and other postretirement benefit liability adjustments arising during the period, tax provision (benefit)			6
Amortization of net loss and prior service credit included in net periodic pension cost , tax provision	$ 1	$ 1	$ 1	$ 1

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Jun. 30, 2015	Sep. 30, 2014
Current assets:
Cash and cash equivalents	$ 84	$ 67
Accounts and notes receivable, net of reserve for doubtful accounts of $8 and $7	563	688
Inventories:
Raw materials	88	111
Work in process	4	2
Finished goods	298	341
Other	42	44
Total inventories	432	498
Prepaid expenses and other current assets	60	69
Deferred income taxes	39	42
Total current assets	1,178	1,364
Property, plant and equipment, net	1,427	1,581
Goodwill	157	536
Equity affiliates	61	68
Intangible assets, net	159	347
Assets held for rent	68	56
Deferred income taxes	137	80
Other assets	49	52
Total assets	3,236	4,084
Current liabilities:
Notes payable	152	44
Accounts payable and accrued liabilities	387	512
Income taxes payable	27	49
Deferred income taxes	1	1
Current portion of long-term debt	1	24
Total current liabilities	568	630
Long-term debt	971	1,004
Deferred income taxes	52	68
Other liabilities	249	291
Redeemable preferred stock	28	27
Commitments and contingencies (Note J)
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: 0 and 64,634,731 shares Outstanding: 0 and 64,382,366 shares	63	64
Less cost of 247,816 and 252,365 shares of common treasury stock	(8)	(7)
Additional paid-in capital		49
Retained earnings	1,464	1,900
Accumulated other comprehensive loss	(255)	(64)
Total Cabot Corporation stockholders' equity	1,264	1,942
Noncontrolling interests	104	122
Total stockholders' equity	1,368	2,064
Total liabilities and stockholders’ equity	$ 3,236	$ 4,084

Consolidated Balance Sheets (Parenthetical) (Unaudited) - USD ($) $ in Millions	Jun. 30, 2015	Sep. 30, 2014
Statement Of Financial Position [Abstract]
Accounts and notes receivable, reserve for doubtful accounts	$ 8	$ 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	63,162,812	64,634,731
Common stock, outstanding shares	62,914,996	64,382,366
Common treasury stock, shares	247,816	252,365

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash Flows from Operating Activities:
Net (loss) income	$ (367)	$ 182
Adjustments to reconcile net income to cash provided (used in) by operating activities:
Depreciation and amortization	140	150
Long-lived asset impairment charge	209	4
Goodwill impairment charge	353
Deferred tax (benefit) provision	(75)	(16)
Gain on step-acquisition		(29)
Employee benefit plan settlement	18
Equity in net (income) loss of affiliated companies	(4)	2
Non-cash compensation	9	11
Other non-cash (income) expense	(3)	1
Changes in assets and liabilities:
Accounts and notes receivable	80	(62)
Inventories	33	(66)
Prepaid expenses and other current assets	4	(20)
Accounts payable and accrued liabilities	(84)
Income taxes payable	(22)	2
Other liabilities	(27)	4
Cash dividends received from equity affiliates	10	22
Other	4
Cash provided by operating activities	278	185
Cash Flows from Investing Activities:
Additions to property, plant and equipment	(103)	(115)
Proceeds from notes receivable from sales of business		215
Change in assets held for rent	(8)	(5)
Cash paid for acquisition of business, net of cash acquired of $7		(73)
Cash (used in) provided by investing activities	(111)	22
Cash Flows from Financing Activities:
Borrowings under financing arrangements		13
Repayments under financing arrangements	(4)	(10)
Increase (decrease) in notes payable, net	1	(11)
Proceeds (repayments) from issuance of commercial paper, net	111	(138)
Proceeds from long-term debt, net of issuance costs		17
Repayments of long-term debt	(57)	(7)
Purchases of common stock	(85)	(6)
Proceeds from sales of common stock	6	13
Cash dividends paid to noncontrolling interests	(16)	(19)
Cash dividends paid to common stockholders	(42)	(40)
Cash used in financing activities	(86)	(188)
Effects of exchange rate changes on cash	(64)	(13)
Increase in cash and cash equivalents	17	6
Cash and cash equivalents at beginning of period	67	95
Cash and cash equivalents at end of period	$ 84	$ 101

Consolidated Statements of Cash Flows (Parenthetical) (Unaudited) $ in Millions	9 Months Ended
	Jun. 30, 2015 USD ($)
Statement Of Cash Flows [Abstract]
Cash acquired in acquisition of business	$ 7

Basis of Presentation	9 Months Ended
Basis of Presentation	Jun. 30, 2015
Accounting Policies [Abstract]
Basis of Presentation	A. Basis of Presentation The consolidated financial statements include the accounts of Cabot Corporation (“Cabot” or the “Company”) 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. Intercompany transactions have been eliminated in consolidation. The unaudited consolidated financial statements have been prepared in accordance with the requirements of Form 10-Q and consequently do not include all disclosures required by Form 10-K. Additional information may be obtained by referring to Cabot’s Annual Report on Form 10-K for the fiscal year ended September 30, 2014 (“2014 10-K”). The financial information submitted herewith is unaudited and reflects all adjustments which are, in the opinion of management, necessary to provide a fair statement of the results for the interim periods ended June 30, 2015 and 2014. All such adjustments are of a normal recurring nature. The results for interim periods are not necessarily indicative of the results to be expected for the fiscal year. In November 2013, the Company purchased all of Grupo Kuo S.A.B. de C.V.’s (“KUO”) common stock in NHUMO, S.A. de C.V. (“NHUMO”), a former carbon black joint venture between the Company and KUO in Mexico, which represented approximately 60% of the outstanding common stock of NHUMO (the “NHUMO transaction”). Prior to this transaction, the Company owned approximately 40% of the outstanding common stock of NHUMO, and the NHUMO entity was accounted for as an equity affiliate of the Company. The financial position, results of operations and cash flows of NHUMO are included in the Company’s consolidated financial statements from the date of acquisition. In July 2014, the Company completed the sale of its Security Materials business. The Consolidated Statements of Operations and the notes to the consolidated financial statements for all periods presented exclude the Security Materials business. In December 2014, the Company realigned its business reporting structure into four segments that consist of Reinforcement Materials, Performance Chemicals, Purification Solutions and Specialty Fluids. The new structure is aligned with senior management changes and it better leverages Cabot’s global activities across common customer applications, production, and research and development activities. Prior period segment results have been recast to reflect the realignment.

Significant Accounting Policies

9 Months Ended

Jun. 30, 2015

Accounting Policies [Abstract]

Significant Accounting Policies

B. Significant Accounting Policies

Revenue Recognition and Accounts Receivable

Cabot recognizes revenue when persuasive evidence of an arrangement exists, delivery has occurred or services have been rendered, the price is fixed or determinable and collectability is reasonably assured. Cabot generally is able to ensure that products meet customer specifications prior to shipment. If the Company is unable to determine that the product has met the specified objective criteria prior to shipment or if title has not transferred because of sales terms, the revenue is considered “unearned” and is deferred until the revenue recognition criteria are met.

Shipping and handling charges related to sales transactions are recorded as sales revenue when billed to customers or included in the sales price.

The following table shows the relative size of the revenue recognized in each of the Company’s reportable segments for the periods presented.

	Three Months Ended June 30						Nine Months Ended June 30
	2015			2014			2015			2014
Reinforcement Materials		52	%		60	%		55	%		59	%
Performance Chemicals		35	%		29	%		33	%		29	%
Purification Solutions		11	%		9	%		10	%		9	%
Specialty Fluids		2	%		2	%		2	%		3	%

Cabot derives the substantial majority of its revenues from the sale of products in Reinforcement Materials and Performance Chemicals. Revenue from these products is typically recognized when the product is shipped and title and risk of loss have passed to the customer. The Company offers certain of its customers cash discounts and volume rebates as sales incentives. Depending on the nature of the contract with the customer, a portion of the revenue may be recognized using proportional performance. The discounts and volume rebates are recorded as a reduction in sales at the time revenue is recognized and are estimated based on historical experience and contractual obligations. Cabot periodically reviews the assumptions underlying its estimates of discounts and volume rebates and adjusts its revenues accordingly.

Revenue in Purification Solutions is typically recognized when the product is shipped and title and risk of loss have passed to the customer. For major activated carbon injection systems projects, revenue is recognized using the percentage-of-completion method.

Revenue in Specialty Fluids arises primarily from the rental of cesium formate. This revenue is recognized throughout the rental period based on the contracted rental terms. Customers are also billed and revenue is recognized, typically at the end of the job, for cesium formate product that is not returned. The Company also generates revenues from cesium formate sold outside of a rental process and revenue is recognized upon delivery of the fluid.

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 is no material off-balance sheet credit exposure related to customer receivable balances.

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. 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, but is reviewed for impairment annually as of May 31, or when events or changes in the business environment indicate that the carrying value of the reporting unit may exceed its fair value. 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. The reporting units with goodwill balances are Reinforcement Materials, Purification Solutions, and Fumed Metal Oxides. The separate businesses included within Performance Chemicals are considered separate reporting units. As such, the goodwill balance relative to this segment is recorded in the Fumed Metal Oxides reporting unit within Performance Chemicals.

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 under the two-step impairment test. 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, the Company performs an analysis of the fair value of all assets and liabilities of the reporting unit. If the implied fair value of the reporting unit’s goodwill is determined to be less than its carrying amount, an impairment is recognized for the difference. The fair value of a reporting unit is based on discounted estimated future cash flows. The fair value is also benchmarked against 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. Should the fair value of any of the Company’s reporting units sufficiently decline because of reduced operating performance, market declines, changes in the discount rate, or other conditions, charges for impairment may be necessary. Based on the Company’s most recent annual goodwill impairment test performed as of May 31, 2015, the fair values of the Reinforcement Materials and Fumed Metal Oxides reporting units were substantially in excess of their carrying values. The fair value of the Purification Solutions reporting unit was less than its carrying amount. Refer to Note F for details on the Purification Solutions goodwill impairment test and the resulting impairment charge recorded.

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 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. The Company evaluates indefinite-lived intangible assets, which are comprised of the trademarks of Purification Solutions, for impairment annually or when events occur or circumstances change that may reduce the fair value of the asset below its carrying amount. The annual review is performed as of May 31. The Company may first perform a qualitative assessment to determine whether it is necessary to perform the quantitative impairment test or bypass the qualitative assessment and proceed directly to performing the quantitative impairment test. The quantitative impairment test is based on discounted estimated future cash flows. The assumptions used to estimate fair value include management’s best estimates of future growth rates and discount rates over an estimate of the remaining operating period at the unit of accounting level. Refer to Note F for details on the impairment test performed on intangible assets of the Purification Solutions reporting unit and the resulting impairment charges recorded. Effective in the third quarter of 2015 and as a part of the impairment assessment performed, the Company determined that the trademarks for Purification Solutions no longer have an indefinite life.

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 F regarding the results of the impairment test performed on the long-lived assets of the Purification Solutions segment.

Property, Plant and Equipment

Property, plant and equipment are recorded at cost. Depreciation of property, plant and equipment is generally calculated using the straight-line method over the estimated useful lives. The depreciable lives for buildings, machinery and equipment, and other fixed assets are twenty to twenty-five years, ten to twenty-five years, and three to 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.

Income Tax in Interim Periods

The Company records its tax provision or benefit on an interim basis using an estimated annual effective tax rate. This rate is applied to the current period ordinary income or loss to determine the income tax provision or benefit allocated to the interim period. Losses from jurisdictions for which no benefit can be recognized and the income tax effects of unusual or infrequent items are excluded from the estimated annual effective tax rate and are recognized in the impacted interim period.

Valuation allowances are provided against the future tax benefits that arise from the deferred tax assets in jurisdictions for which no benefit can be recognized. The estimated annual effective tax rate may be significantly impacted by nondeductible expenses and the Company’s projected earnings mix by tax jurisdiction. Adjustments to the estimated annual effective income tax rate are recognized in the period when such estimates are revised.

Inventory Valuation

Inventories are stated at the lower of cost or market. The cost of all carbon black inventories in the U.S. is determined using the last-in, first-out (“LIFO”) method. Had the Company used the first-in, first-out (“FIFO”) method instead of the LIFO method for such inventories, the value of those inventories would have been $37 million and $52 million higher as of June 30, 2015 and September 30, 2014, respectively. The cost of Specialty Fluids inventories is determined using the average cost method. The cost of other U.S. and non-U.S. inventories is determined using the FIFO method.

Cabot 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 market value.

Pensions and Other Postretirement Benefits

The Company recognizes the funded status of defined benefit pension and other postretirement benefit plans as an asset or liability. This amount is defined as the difference between the fair value of plan assets and the benefit obligation. The Company is required to recognize as a component of other comprehensive income, net of tax, the actuarial gains/losses and prior service costs/credits that arise but were not previously required to be recognized as components of net periodic benefit cost. Other comprehensive income is adjusted as these amounts are later recognized in income as components of net periodic benefit cost.

Accumulated Other Comprehensive (Loss) Income

Accumulated other comprehensive (loss) income (“AOCI”), which is included as a component of stockholders’ equity, includes unrealized gains or losses on available-for-sale marketable securities, currency translation adjustments in foreign subsidiaries, translation adjustments on foreign equity securities and pension liability adjustments.

Recent Accounting Pronouncements

In July 2013, the Financial Accounting Standards Board (“FASB”) issued a new standard related to the “Presentation of an Unrecognized Tax Benefit When a Net Operating Loss Carryforward, a Similar Tax Loss, or a Tax Credit Carryforward Exists”. The standard requires, unless certain conditions exist, an unrecognized tax benefit or a portion of an unrecognized tax benefit to be presented in the consolidated financial statements as a reduction to a deferred tax asset for a net operating loss carryforward, similar to a tax loss or a tax credit carryforward. This standard is applicable for fiscal years beginning after December 15, 2013, and for interim periods within those years. The Company adopted this standard on October 1, 2014 and the implementation of the new standard did not have a material impact on its consolidated financial statements.

In April 2014, the FASB issued a new standard related to “Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity”. The standard requires discontinued operations treatment for disposals of a component or group of components of a business that represents a strategic shift that has or will have a major impact on an entity’s operations or financial results and requires additional disclosures for discontinued operations and new disclosures for individually material disposal transactions that do not meet the definition of a discontinued operation. This standard is applicable for fiscal years beginning after December 15, 2014 and for interim periods within those years and early adoption is permitted, but only for disposals that have not been reported in consolidated financial statements previously issued. The Company expects to adopt this standard beginning on October 1, 2015.

In May 2014, the FASB issued a new standard related to the “Revenue from Contracts with Customers” which amends 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. This standard is applicable for fiscal years beginning after December 15, 2017 and for interim periods within those years and early adoption is permitted for the fiscal years beginning after December 15, 2016. The Company expects to adopt this standard on October 1, 2018. The Company is currently evaluating the impact of the adoption of this standard on its consolidated financial statements.

In April 2015, the FASB issued a new standard simplifying the presentation of debt issuance costs by requiring debt issuance costs to be presented as a reduction of the corresponding debt liability. This will make the presentation of debt issuance costs consistent with the presentation of debt discounts or premiums. This standard is applicable for fiscal years beginning after December 15, 2015 and for interim periods within those years and early adoption is permitted. The Company expects to adopt this standard on October 1, 2016. The adoption of this standard is not expected to materially impact the Company’s consolidated financial statements.

Acquisition of NHUMO

9 Months Ended

Jun. 30, 2015

Business Combinations [Abstract]

Acquisition of NHUMO

C. Acquisition of NHUMO

In November 2013, the Company purchased all of KUO’s common stock in the former NHUMO joint venture, which represented approximately 60% of the outstanding common stock of the joint venture. Prior to this transaction, the Company owned approximately 40% of the outstanding common stock of NHUMO, and the NHUMO entity was accounted for as an equity affiliate of the Company.

At the close of the transaction, the Company paid KUO $80 million in cash and NHUMO issued redeemable preferred stock to KUO with a redemption value of $25 million. The preferred stock accumulates dividends at a fixed rate of 6% annually and is redeemable at the option of KUO or the Company for $25 million starting in November 2018 or upon the occurrence of certain other conditions. Annual payment by NHUMO of the dividends is contingent on NHUMO achieving a minimum EBITDA (earnings before interest, taxes, depreciation and amortization) level and if such minimum EBITDA is not achieved in any year, the dividend will be accumulated and paid at the time the preferred shares are redeemed. The minimum EBITDA was achieved in 2014 and a dividend payment of $1.5 million was made in December 2014. The preferred stock issued in connection with the transaction is not mandatorily redeemable and has embedded put and call rights at the fixed redemption price. Accordingly, the instrument is accounted for as a financing obligation and has been separately presented in the Consolidated Balance Sheets as a long-term liability. Upon acquisition, the Company began consolidating NHUMO into its consolidated financial statements. Prior to closing, the Company received a $14 million dividend from NHUMO.

As of September 2014, the Company completed the valuation of its assets acquired and liabilities assumed. The allocation of the purchase price is based on the fair value of assets acquired and liabilities assumed, and Cabot’s previously held equity interest in NHUMO as of the acquisition date. The following table presents the components and allocation of the purchase price:

	(Dollars in millions)
Assets
Current assets	$	54
Property, plant and equipment		48
Other non-current assets		1
Intangible assets		63
Goodwill		45
Total assets acquired		211
Liabilities
Accounts payable, accruals and other liabilities		(20	)
Deferred tax liabilities - long-term		(29	)
Total liabilities assumed		(49	)
Net assets acquired	$	162
Cash consideration paid		80
Fair value of redeemable preferred stock		28
Previously held equity interest in NHUMO		54
Total	$	162

As a result of the acquisition, the Company recorded a gain of $29 million for the difference between the carrying value and the fair value of the previously held equity interest in NHUMO, which was included in Other (expense) income in the first quarter of fiscal 2014. The fair value of $54 million for the previously held equity interest was determined based on the fair value of Cabot’s pre-existing interest in NHUMO as adjusted for a control premium derived from synergies gained as a result of the Company obtaining control of NHUMO.

As part of the purchase price allocation, the Company determined that a separately identifiable intangible asset was customer relationships in the amount of $63 million, which is being amortized over a period of 20 years. The Company estimated the fair value of the identifiable acquisition-related intangible asset based on projections of cash flows that will arise from the asset. The projected cash flows are discounted to determine the fair value of the asset at the date of acquisition. The determination of the fair value of the intangible asset acquired required the use of significant judgment with regard to assumptions in the discounted cash flow model used.

The fair value of the redeemable preferred stock was determined based on a discounted cash flow model, using the expected timing of the cash flows and an appropriate discount rate.

The excess of the purchase price, which includes the cash consideration paid and the fair values of redeemable preferred stock and the previously held equity interest in NHUMO, over the fair value of the tangible net assets and intangible asset acquired, was recorded as goodwill. The goodwill recognized is attributable to the expected growth and operating synergies that the Company expects to realize from this acquisition. Goodwill generated from the acquisition is not deductible for tax purposes.

Discontinued Operations	9 Months Ended
Discontinued Operations	Jun. 30, 2015
Discontinued Operations And Disposal Groups [Abstract]
Discontinued Operations	D. Discontinued Operations In July 2014, the Company sold its Security Materials business to SICPA SA. The Consolidated Statements of Operations for all periods presented have been recast to reflect the Security Materials business in discontinued operations. During the third quarter of fiscal 2015, Cabot recorded a tax benefit in the amount of $1 million related to the sale of the business, which was included in the Company’s 2014 tax return.

- Definition

The entire disclosure related to a disposal group. Includes, but is not limited to, a discontinued operation, disposal classified as held-for-sale or disposed of by means other than sale or disposal of an individually significant component.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 11
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+ Details

Employee Benefit Plans

9 Months Ended

Jun. 30, 2015

Compensation And Retirement Disclosure [Abstract]

Employee Benefit Plans

E. Employee Benefit Plans

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

	Three Months Ended June 30
	2015						2014						2015					2014
	Pension Benefits												Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign		U.S.			Foreign
	(Dollars in millions)
Service cost	$	—		$	2		$	1		$	2		$	—		$	—	$	—		$	—
Interest cost		2			3			2			4			—			1		1			1
Expected return on plan assets		(3	)		(4	)		(3	)		(5	)		—			—		—			—
Amortization of prior service credit		—			—			—			—			(1	)		—		(1	)		—
Amortization of actuarial loss		—			1			—			1			—			—		—			—
Net periodic benefit (credit) cost	$	(1	)	$	2		$	—		$	2		$	(1	)	$	1	$	—		$	1

	Nine Months Ended June 30
	2015						2014						2015					2014
	Pension Benefits												Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign		U.S.			Foreign
	(Dollars in millions)
Service cost	$	—		$	7		$	2		$	7		$	—		$	—	$	—		$	—
Interest cost		5			9			6			12			1			1		2			1
Expected return on plan assets		(8	)		(12	)		(8	)		(15	)		—			—		—			—
Amortization of prior service credit		—			—			—			—			(2	)		—		(2	)		—
Amortization of actuarial loss		—			3			—			3			—			—		—			—
Settlement costs		—			18			—			—			—			—		—			—
Net periodic benefit (credit) cost	$	(3	)	$	25		$	—		$	7		$	(1	)	$	1	$	—		$	1

Settlement of employee benefit plan

Effective October 1, 2014, 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 decision effectively moves the administrative, asset custodial, asset investment, actuarial, communication and benefit payment obligations to the multi-employer fund administrator. The plan is over 80% funded. Cabot is required to make contributions to the multi-employer fund and assets contributed by one participating employer may be used to provide benefits to employees of other participating employers since assets contributed by an employer are not segregated in a separate account or restricted to provide benefits only to employees of that employer. As a result of the transfer, a pre-tax charge of $18 million has been recorded in the nine months ended June 30, 2015 as reflected in Settlement costs in the table above. The pre-tax charge consists of $27 million released from AOCI and $2 million of employer contributions at the time of the settlement, partially offset by an $11 million release of the pension liability. The settlement charge has been recorded primarily in Cost of sales in the Consolidated Statements of Operations.

Purification Solutions Goodwill and Long-Lived Assets Impairment Charges

9 Months Ended

Jun. 30, 2015

Goodwill And Intangible Assets Disclosure [Abstract]

Purification Solutions Goodwill and Long-Lived Assets Impairment Charges

F. Purification Solutions Goodwill and Long-Lived Assets Impairment Charges

During the third quarter of fiscal 2015 and as a result of the impairment tests performed on goodwill and long-lived assets of the Purification Solutions reporting unit, the Company recorded impairment charges and an associated tax benefit in the Consolidated Statements of Operations as follows:

	June 30, 2015
		(Dollars in millions)
Goodwill impairment charge	$	353
Long-lived assets impairment charge		209
Provision (benefit) for income taxes		(80	)
Impairment charges, after tax	$	482

The future growth in the Purification Solutions segment is highly dependent on achieving the expected volumes and margins in the activated carbon based mercury removal business. These volumes and margins are highly dependent on demand for mercury removal products and the Company’s successful realization of its anticipated share of volumes in this business. The expected demand for mercury removal products significantly depends on: (1) the implementation and enforcement of environmental laws and regulations, particularly those that would require U.S. based coal-fired electric utilities to reduce the quantity of air pollutants they release, including mercury, to comply with the Mercury and Air Toxics Standards (“MATS”) issued by the U.S. Environmental Protection Agency (“EPA”) and (2) other factors such as the anticipated usage of activated carbon in the coal-fired energy units. In November 2014, the U.S. Supreme Court agreed to consider whether the EPA appropriately considered costs in determining whether it is necessary and appropriate to regulate hazardous air pollutants emitted by electric utilities. On June 29, 2015, the U.S. Supreme Court held that the EPA unreasonably failed to consider costs in determining whether it is necessary and appropriate to regulate hazardous air pollutants emitted by coal-fired utilities, and remanded the case back to the D.C. Circuit Court of Appeals for further proceedings.

The implementation period for the MATS regulations began in April 2015. With this recent implementation and associated customer and industry developments during the quarter, as well as the U.S. Supreme Court’s ruling, the Company reassessed its previous estimates for expected growth in volumes, prices and margins in the Purification Solutions reporting unit. The main drivers of growth, including the size of the overall mercury removal industry, utility adoption rates, usage levels, and pricing, among others, were lowered. Based on these revised estimates and as part of step one of the annual impairment test, the Company determined that the estimated fair value of the Purification Solutions reporting unit was lower than the reporting unit's carrying value. As such, the reporting unit failed step one of the goodwill impairment test.

In determining the fair value of the Purification Solutions reporting unit, the Company used an income approach (a discounted cash flow analysis) which incorporated significant estimates and assumptions related to future periods, including timing of MATS implementation, the anticipated size of the mercury removal industry, and growth rates and pricing assumptions of activated carbon, among others. The Company assumed a two year delay in the MATS implementation due to the U.S. Supreme Court’s ruling. Total charges incurred could be higher if the rulings of the D.C. Circuit Court of Appeals on remand result in a delay in the implementation of MATS that is longer than two years. In addition, an estimate of the reporting unit’s weighted average cost of capital (“WACC”) is used to discount future estimated cash flows to their present value. The WACC was based upon externally available data considering market participants’ cost of equity and debt, optimal capital structure and risk factors specific to the Purification Solutions reporting unit.

Step two of the goodwill impairment test requires the Company to perform a theoretical purchase price allocation for the reporting unit to determine the implied fair value of goodwill and to compare the implied fair value of goodwill to the recorded amount of goodwill. The estimate of fair value is complex and requires significant judgment. Accounting guidance provides that a company should recognize an estimated impairment charge to the extent that it determines that it is probable that an impairment loss has occurred and such impairment can be reasonably estimated. Based on the best estimate as of June 30, 2015, the Company recorded a pre-tax goodwill impairment charge of $353 million.

Based on the same factors leading to goodwill impairment, the Company also considered whether the reporting unit's carrying values of definite-lived intangible assets and property, plant and equipment may not be recoverable or whether the carrying value of certain indefinite-lived intangible assets were impaired. The Company used the income approach to determine the fair value of the indefinite-lived intangible assets, which are the trademarks of Purification Solutions, and determined that the fair value of these intangible assets was lower than their carrying value. As such, an impairment loss was recorded in the amount of $39 million. Subsequent to this impairment analysis, the Company concluded that such assets no longer had an indefinite life and began amortizing these assets over their estimated useful life. The Company also performed an impairment analysis to assess if definite-lived intangible assets and property, plant and equipment were recoverable 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, an impairment charge was recorded based on the lower of the carrying amount or fair value of the long-lived assets. The Company used the income approach to determine the fair value of the definite-lived intangible assets and a combination of the cost and market approaches to fair value its property, plant and equipment. The Company recorded impairment charges of $119 million and $51 million, to its definite-lived intangible assets and property, plant and equipment, respectively, in the quarter ended June 30, 2015.

In connection with the long-lived assets impairment charges, the Company recorded a deferred tax benefit of $80 million to its income tax provision.

Due to the complexities involved in estimating fair value and the recent issuance of the U.S. Supreme Court’s ruling, the Company has not completed the step two analysis and expects to finalize it in the fourth quarter of fiscal 2015. Total impairment charges are not expected to materially change.

The performance of the Purification Solutions reporting unit will continue to be monitored. If the reporting unit does not achieve the financial performance that the Company expects or events or circumstances change, it is possible that additional impairment charges may result.

Goodwill and Intangible Assets

9 Months Ended

Jun. 30, 2015

Goodwill And Intangible Assets Disclosure [Abstract]

Goodwill and Intangible Assets

G. Goodwill and Intangible Assets

Cabot had goodwill balances of $157 million and $536 million at June 30, 2015 and September 30, 2014, respectively. The carrying amount of goodwill attributable to each reportable segment with goodwill balances and the changes in those balances during the period ended June 30, 2015 are as follows:

	Reinforcement Materials			Performance Chemicals			Purification Solutions			Total
	(Dollars in millions)
Balance at September 30, 2014	$	68		$	10		$	458		$	536
Impairment charge		—			—			(353	)		(353	)
Foreign currency impact		(9	)		(1	)		(16	)		(26	)
Balance at June 30, 2015	$	59		$	9		$	89		$	157

Goodwill impairment tests are performed at least annually. The Company performed its last annual impairment assessment as of May 31, 2015 and determined there was an impairment of the assets attributable to the Purification Solutions reporting unit. Refer to Note F.

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

	June 30, 2015							September 30, 2014
	Gross Carrying Value		Accumulated Amortization			Net Intangible Assets		Gross Carrying Value		Accumulated Amortization			Net Intangible Assets
	(Dollars in millions)
Intangible assets with finite lives⁽¹⁾
Developed technologies	$	48	$	—		$	48	$	152	$	(16	)	$	136
Trademarks		16		—			16		57		—			57
Customer relationships		100		(5	)		95		171		(17	)		154
Total intangible assets	$	164	$	(5	)	$	159	$	380	$	(33	)	$	347

⁽¹⁾	Refer to Note F for intangible assets impairment charges recorded in the third fiscal quarter of 2015.

Intangible assets are amortized over their estimated useful lives, which range from fourteen to twenty-five years, with a weighted average amortization period of approximately nineteen years. Amortization expense for the three months ended June 30, 2015 and 2014 was $3 million and $4 million, respectively, and is included in Cost of sales and Selling and administrative expenses in the Consolidated Statements of Operations. Amortization expense for the nine months ended June 30, 2015 and 2014 was $12 million and $13 million, respectively, and is included in Cost of sales and Selling and administrative expenses in the Consolidated Statements of Operations. Total amortization expense is estimated to be approximately $9 million each year for the next five fiscal years.

- Definition

The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final. May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.

+ References + Details

Stockholders' Equity

9 Months Ended

Jun. 30, 2015

Equity [Abstract]

Stockholders' Equity

H. Stockholders’ Equity

In fiscal 2007, the Board of Directors authorized Cabot to repurchase up to ten million shares of Cabot’s common stock in the open market or in privately negotiated transactions. This authorization did not have a set expiration date. During the first nine months of fiscal 2015 and 2014, Cabot repurchased 925,700 and 379 shares, respectively, of its common stock under this authorization.

In January 2015, the Board of Directors authorized Cabot to repurchase up to five million shares of the Company’s common stock in the open market or in privately negotiated transactions and cancelled the previous authorization. Cabot has repurchased 874,300 shares of its common stock under this authorization. As of June 30, 2015, approximately 4,125,700 shares remain available for repurchase under the current authorization. The Company retired the repurchased shares and recorded the excess of the purchase price over par value to additional paid-in capital until such amount was reduced to zero and then charged the remainder against retained earnings.

During the first nine months of fiscal 2015, Cabot paid cash dividends of $0.66 per share of common stock for a total of $42 million. During the first nine months of fiscal 2014, Cabot paid cash dividends of $0.62 per share of common stock for a total of $40 million.

Noncontrolling interest

The following table illustrates the noncontrolling interest activity for the periods presented:

	2015			2014
	(Dollars in millions)
Balance at September 30	$	122		$	132
Net income attributable to noncontrolling interest		7			14
Noncontrolling interest foreign currency translation adjustment		(3	)		(2	)
Noncontrolling interest dividends		(22	)		(25	)
Balance at June 30	$	104		$	119

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section E

Reference 15: http://www.xbrl.org/2003/role/presentationRef
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-Number Topic 4
-Section C

+ Details

Accumulated Other Comprehensive Loss

9 Months Ended

Jun. 30, 2015

Equity [Abstract]

Accumulated Other Comprehensive Loss

I. Accumulated Other Comprehensive Loss

Comprehensive income combines net (loss) income and other comprehensive income items, which are reported as components of stockholders’ equity in the accompanying Consolidated Balance Sheets.

Changes in each component of AOCI, net of tax, are as follows:

						Pension and Other
	Currency			Unrealized		Postretirement
	Translation			Gains on		Benefit Liability
	Adjustment			Investments		Adjustments			Total
	(Dollars in millions)
Balance at September 30, 2014, attributable to Cabot Corporation	$	27		$	2	$	(93	)	$	(64	)
Other comprehensive loss before reclassifications		(103	)		—		—			(103	)
Amounts reclassified from accumulated other comprehensive income		—			—		21			21
Net other comprehensive items		(103	)		—		21			(82	)
Less: Noncontrolling interest		(2	)		—		—			(2	)
Balance at December 31, 2014, attributable to Cabot Corporation	$	(74	)	$	2	$	(72	)	$	(144	)
Other comprehensive loss before reclassifications		(131	)		—		—			(131	)
Amounts reclassified from accumulated other comprehensive income		—			—		1			1
Net other comprehensive items		(131	)		—		1			(130	)
Less: Noncontrolling interest		(1	)		—		—			(1	)
Balance at March 31, 2015, attributable to Cabot Corporation	$	(204	)	$	2	$	(71	)	$	(273	)
Other comprehensive income before reclassifications		18			—		—			18
Amounts reclassified from accumulated other comprehensive income		—			—		—			—
Net other comprehensive items		18			—		—			18
Less: Noncontrolling interest		—			—		—			—
Balance at June 30, 2015, attributable to Cabot Corporation	$	(186	)	$	2	$	(71	)	$	(255	)

Accumulated other comprehensive items in the accompanying Consolidated Balance Sheets consist of the following items, net of tax:

	June 30,			September 30,
	2015			2014
	(Dollars in millions)
Foreign currency translation adjustments at beginning of period	$	27		$	154
Net foreign currency translation adjustments attributable to Cabot during the period		(213	)		(127	)
Balance at end of period		(186	)		27
Unrealized gain on investments at beginning of period		2			2
Net unrealized gains during the period		—			—
Balance at end of period		2			2
Pension and other postretirement benefit plans attributable to Cabot at beginning of period		(93	)		(53	)
Net change in pension and other postretirement benefit plans during the period		22			(40	)
Balance at end of period		(71	)		(93	)
Total accumulated other comprehensive loss	$	(255	)	$	(64	)

The amounts reclassified out of AOCI and into the Consolidated Statements of Operations for the three and nine months ended June 30, 2015 and 2014 are as follows:

		Three Months Ended						Nine Months Ended
	Affected Line Item in the Consolidated	June 30,						June 30,
	Statements of Operations	2015			2014			2015			2014
		(Dollars in millions)
Pension and other postretirement benefit liability adjustment
Amortization of actuarial losses	Net Periodic Benefit Cost - see Note E for details	$	1		$	1		$	3		$	3
Amortization of prior service cost	Net Periodic Benefit Cost - see Note E for details		(1	)		(1	)		(2	)		(2	)
Settlement costs	Net Periodic Benefit Cost - see Note E for details		—			—			27			—
Total before tax			—			—			28			1
Tax impact	Benefit for income taxes		—			—			(6	)		—
Total after tax		$	—		$	—		$	22		$	1

- Definition

The entire disclosure for comprehensive income, which includes, but is not limited to, 1) the amount of income tax expense or benefit allocated to each component of other comprehensive income, including reclassification adjustments, 2) the reclassification adjustments for each classification of other comprehensive income and 3) the ending accumulated balances for each component of comprehensive income.

+ References

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-Publisher FASB
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
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Reference 8: http://www.xbrl.org/2003/role/presentationRef
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Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Reclassification Adjustments
-URI http://asc.fasb.org/extlink&oid=6522872

+ Details

Commitments and Contingencies

9 Months Ended

Jun. 30, 2015

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

J. Commitments and Contingencies

Purchase 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. For those commitments, the amounts included in the table below are based on market prices at June 30, 2015.

	Payments Due by Fiscal Year
	Remainder of Fiscal 2015		2016		2017		2018		2019		Thereafter		Total
	(Dollars in millions)
Reinforcement Materials	$	86	$	227	$	178	$	177	$	173	$	1,911	$	2,752
Performance Chemicals		19		60		38		33		33		210		393
Purification Solutions		7		13		9		7		7		8		51
Total	$	112	$	300	$	225	$	217	$	213	$	2,129	$	3,196

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.

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 June 30, 2015 and September 30, 2014, Cabot had $16 million and $17 million, respectively, reserved for environmental matters, substantially all of which is accounted for on an undiscounted basis. These environmental matters mainly relate to closed sites. These reserves 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. Cash payments related to these environmental matters were $1 million and $2 million in the first nine months of fiscal 2015 and 2014, respectively. 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.

Other Matters

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 Cabot 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. As more fully described in the 2014 10-K, the respirator liabilities generally 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.

As of June 30, 2015 and September 30, 2014, there were approximately 38,000 and 41,000 claimants, respectively, in pending cases asserting claims against AO in connection with respiratory products. Cabot has a reserve to cover its expected share of liability for existing and future respirator liability claims. At June 30, 2015 and September 30, 2014, the reserve was $11 million and $13 million, respectively. Cash payments related to this liability were $2 million in the first nine months of both fiscal 2015 and 2014.

Other

The Company is subject to various other lawsuits, claims and contingent liabilities arising in the ordinary course of its business and with respect to the Company’s divested businesses. In the opinion of the Company, although final disposition of some or all of these other suits and claims may impact the Company’s consolidated financial statements in a particular period, they are not expected, in the aggregate, to have a material adverse effect on the Company’s financial position.

Income Tax

9 Months Ended

Jun. 30, 2015

Income Tax Disclosure [Abstract]

Income Tax

K. Income Tax

Effective Tax Rate

	Three Months Ended June 30						Nine Months Ended June 30
	2015			2014			2015			2014
	(Dollars in millions)						(Dollars in millions)
(Benefit) Provision for income taxes	$	(64	)	$	20		$	(47	)	$	51
Effective tax rate		13	%		25	%		11	%		22	%

During the third quarter of fiscal 2015, the Company recorded charges related to the impairment of goodwill and long-lived assets of the Purification Solutions segment as disclosed in Note F. Prior to the impairment, the Company had recorded deferred tax liabilities for the difference in the tax basis and book basis for certain of these long-lived assets. As a result of the $209 million impairment charge and reduction in the book basis of these assets, the Company recorded a corresponding decrease in deferred tax liabilities, as there was no change in tax basis of these assets due to the book impairment, and recorded a tax benefit of $80 million. The $353 million goodwill impairment charge was related to goodwill, which is non-deductible for tax purposes, and therefore there was no tax impact related to this impairment charge. As a result, the Company’s effective tax rate was significantly lower for both the three and nine month periods ending June 30, 2015 than for the comparable periods in fiscal 2014.

Uncertainties

Cabot files U.S. federal and state and non-U.S. income tax returns in jurisdictions with varying statutes of limitations. The 2012 through 2014 tax years remain subject to examination by the United States Internal Revenue Service (“IRS”) and various tax years from 2005 through 2014 remain subject to examination by the respective state tax authorities. In significant non-U.S. jurisdictions, various tax years from 2004 through 2014 remain subject to examination by their respective tax authorities. Cabot’s significant non-U.S. jurisdictions include China, France, Germany, Italy, Japan, and the Netherlands.

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

During the three and nine months ended June 30, 2015, Cabot released uncertain tax positions of less than $1 million and approximately $13 million, respectively, due to the expirations of statutes of limitations in various jurisdictions. As of October 1, 2014, Cabot adopted a new accounting standard which requires, unless certain conditions exist, an unrecognized tax benefit or a portion of an unrecognized tax benefit be presented in the consolidated financial statements as a reduction to a deferred tax asset for a net operating loss carryforward, similar to a tax loss or a tax credit carryforward. This resulted in a reduction of the liability for uncertain tax positions and deferred tax assets of $5 million.

Earnings Per Share

9 Months Ended

Jun. 30, 2015

Earnings Per Share [Abstract]

Earnings Per Share

L. Earnings Per Share

The following tables summarize the components of the basic and diluted earnings per common share computations:

	Three Months Ended June 30						Nine Months Ended June 30
	2015			2014			2015			2014
	(Dollars and shares in millions, except per share amounts)
Basic EPS:
Net (loss) income attributable to Cabot Corporation	$	(445	)	$	52		$	(374	)	$	168
Less: Dividends and dividend equivalents to participating securities		—			—			—			—
Less: Undistributed earnings allocated to participating securities⁽¹⁾		—			1			—			2
(Loss) earnings allocated to common shareholders (numerator)	$	(445	)	$	51		$	(374	)	$	166
Weighted average common shares and participating securities outstanding		63.8			65.1			64.2			64.9
Less: Participating securities⁽¹⁾		0.5			0.6			0.5			0.6
Adjusted weighted average common shares (denominator)		63.3			64.5			63.7			64.3
Amounts per share - basic:
(Loss) income from continuing operations attributable to Cabot Corporation	$	(7.05	)	$	0.80		$	(5.89	)	$	2.61
Income (loss) from discontinued operations		0.01			(0.01	)		0.01			(0.03	)
Net (loss) income attributable to Cabot Corporation	$	(7.04	)	$	0.79		$	(5.88	)	$	2.58
Diluted EPS⁽²⁾:
(Loss) earnings allocated to common shareholders	$	(445	)	$	51		$	(374	)	$	166
Plus: (Loss) earnings allocated to participating securities		—			1			—			2
Less: Adjusted earnings allocated to participating securities⁽³⁾		—			(1	)		—			(2	)
(Loss) earnings allocated to common shareholders (numerator)	$	(445	)	$	51		$	(374	)	$	166
Adjusted weighted average common shares outstanding		63.3			64.5			63.7			64.3
Effect of dilutive securities:
Common shares issuable⁽⁴⁾		—			0.7			—			0.7
Adjusted weighted average common shares (denominator)		63.3			65.2			63.7			65.0
Amounts per share - diluted:
(Loss) income from continuing operations attributable to Cabot Corporation	$	(7.05	)	$	0.79		$	(5.89	)	$	2.58
Income (loss) from discontinued operations		0.01			(0.01	)		0.01			(0.03	)
Net (loss) income attributable to Cabot Corporation	$	(7.04	)	$	0.78		$	(5.88	)	$	2.55

⁽¹⁾	Participating securities consist of shares of unvested restricted stock and unvested time-based restricted stock 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:

	Three Months Ended June 30					Nine Months Ended June 30
	2015			2014		2015			2014
	(Dollars in millions)
Calculation of undistributed (loss) earnings:
Net (loss) income attributable to Cabot Corporation	$	(445	)	$	52	$	(374	)	$	168
Less: Dividends declared on common stock		14			14		42			40
Less: Dividends declared on participating securities		—			—		—			—
Undistributed (loss) earnings	$	(459	)	$	38	$	(416	)	$	128
Allocation of undistributed (loss) earnings:
Undistributed (loss) earnings allocated to common shareholders	$	(459	)	$	37	$	(416	)	$	126
Undistributed (loss) earnings allocated to participating shareholders		—			1		—			2
Undistributed (loss) earnings	$	(459	)	$	38	$	(416	)	$	128

⁽²⁾	Due to the Company’s net loss position, dividends on participating securities were not added back to loss available to common shares for the three and nine months ended June 30, 2015 when calculating diluted EPS.

⁽³⁾	Undistributed earnings are adjusted for the assumed distribution of dividends to the dilutive securities, which are described in (4) below, and then reallocated to participating securities.

⁽⁴⁾

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 Deferred Compensation and Supplemental Retirement Plan; and (iii) assumed issuance of shares under outstanding performance-based restricted stock unit awards issued under Cabot’s equity incentive plans. The weighted average common shares outstanding for the quarter and nine months ending June 30, 2015 excludes 492,172 and 508,991 shares, respectively, as those shares would be antidilutive due to the Company’s net loss position. For the three and nine months ended June 30, 2014, 142,115 and 203,019 incremental shares of common stock, respectively, were not included in the calculation of diluted earnings per share because the inclusion of these shares would have been antidilutive.

Restructuring

9 Months Ended

Jun. 30, 2015

Restructuring And Related Activities [Abstract]

Restructuring

M. Restructuring

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

	Three Months Ended June 30				Nine Months Ended June 30
	2015		2014		2015		2014
	(Dollars in millions)
Cost of sales	$	1	$	2	$	4	$	11
Selling and administrative expenses		1		2		10		13
Total	$	2	$	4	$	14	$	24

Details of these restructuring activities and the related reserves during the three months ended June 30, 2015 are as follows:

	Severance and Employee Benefits			Environmental Remediation		Other		Total
	(Dollars in millions)
Reserve at March 31, 2015	$	9		$	3	$	1	$	13
Charges		2			—		—		2
Cash paid		(5	)		—		—		(5	)
Reserve at June 30, 2015	$	6		$	3	$	1	$	10

Details of these restructuring activities and the related reserves during the nine months ended June 30, 2015 are as follows:

	Severance and Employee Benefits			Environmental Remediation		Asset Impairment and Accelerated Depreciation			Other			Total
	(Dollars in millions)
Reserve at September 30, 2014	$	16		$	2	$	—		$	1		$	19
Charges		7			1		1			5			14
Costs charged against assets / liabilities		—			—		(1	)		—			(1	)
Cash paid		(15	)		—		—			(5	)		(20	)
Foreign currency translation adjustment		(2	)		—		—			—			(2	)
Reserve at June 30, 2015	$	6		$	3	$	—		$	1		$	10

Business Service Center Transition

In January 2014, the Company announced its intention to open a new Europe, Middle East and Africa (“EMEA”) business service center in Riga, Latvia, and to close its Leuven, Belgium site, subject to the Belgian information and consultation process, which was completed in June 2014. These actions were developed following an extensive evaluation of the Company’s business service capabilities in the EMEA region and a determination that the future EMEA business service center will enable the Company to provide the highest quality of service at the most competitive cost.

The Company expects that the majority of actions related to the transition of the business service center will be completed by the end of fiscal 2015 and result in total charges of approximately $24 million, comprised of $16 million of severance charges and $8 million of other transition costs. Through June 30, 2015, the Company has recorded $23 million for this plan comprised of $16 million of severance charges and $7 million of other transition costs

The Company has recorded $5 million and $15 million of charges in the first nine months of fiscal 2015 and 2014, respectively related to this plan. Fiscal 2014 costs included employee severance costs of $14 million and $1 million of other transition costs, whereas fiscal 2015 costs include severance charges of $1 million and $4 million of other transition costs including training costs and redundant salaries. The Company has recorded $1 million of charges in both of the three months ended June 30, 2015 and 2014, respectively, related to this plan, comprised of severance and other transition costs.

Cumulative cash outlays related to this plan are expected to be approximately $22 million, comprised of $14 million of severance payments and $8 million of transition costs. Through June 30, 2015, the Company has made $19 million in cash payments related to this plan, comprised of $7 million of transition costs and $12 million of severance costs, and expects to make additional cash payments of approximately $3 million during the remainder of fiscal 2015 and thereafter, comprised of $2 million of severance costs and $1 million of other transition costs.

As of June 30, 2015, Cabot has $3 million of accrued restructuring costs in the Consolidated Balance Sheet related to this closure.

Closure of Port Dickson, Malaysia Manufacturing Facility

On April 26, 2013, the Company announced that the Board of its carbon black joint venture, Cabot Malaysia Sdn. Bhd. (“CMSB”), decided to cease production at its Port Dickson, Malaysia facility. The facility ceased production in June 2013. The Company holds a 50.1 percent equity share in CMSB. The decision, which affected approximately 90 carbon black employees, was driven by the facility’s manufacturing inefficiencies and raw materials costs.

Through June 30, 2015, the Company recorded pre-tax restructuring charges related to this plan of $18 million comprised mainly of accelerated depreciation and asset write-offs of $15 million, severance charges of $2 million, site demolition, clearing and environmental remediation charges of $2 million, and other closure related charges of $1 million, partially offset by the anticipated gain from the sale of land of $2 million in fiscal 2016. CMSB’s net income or loss is attributable to Cabot Corporation and to the noncontrolling interest in the joint venture. The Company has recorded pre-tax charges of less than $1 million and $2 million in the nine months ended June 30, 2015 and 2014, respectively, related to this closure and less than $1 million in both of three months ended June 30, 2015 and 2014, respectively. The portion of the charges that are allocable to the noncontrolling interest in CMSB (49.9%) are recorded within Net income attributable to noncontrolling interests, net of tax, in the Consolidated Statements of Operations. The majority of actions related to closure of the plant were completed in fiscal 2014.

Cumulative cash outlays related to this plan are expected to be approximately $5 million comprised primarily of $2 million for site demolition, clearing and environmental remediation, $2 million for severance, and $1 million for other closure related charges. Through June 30, 2015, CMSB has made approximately $4 million in cash payments related to this plan mainly for severance and site demolition and clearing costs.

CMSB expects to make cash payments of $1 million during the remainder of fiscal 2015 and thereafter mainly for site demolition, clearing and environmental remediation costs. Approximately $8 million is expected to be received from the sale of land in fiscal 2016.

As of June 30, 2015, Cabot has $1 million of accrued restructuring costs in the Consolidated Balance Sheets related to this closure, which is mainly for accrued environmental and other charges.

Other Activities

The Company has recorded pre-tax charges of approximately $6 million during both of the first nine months of fiscal 2015 and 2014, respectively, and $1 million and $2 million for the three months ended June 30, 2015 and 2014, respectively, related to restructuring activities at several other locations. Fiscal 2015 charges are comprised of severance costs whereas fiscal 2014 charges are comprised of accelerated depreciation, asset write-offs, and severance costs. The Company anticipates that it will record additional charges of $1 million in the remainder of fiscal 2015 related to these actions.

The Company made payments of $4 million related to these actions in the first nine months of fiscal 2015 and expects to pay $5 million in the remainder of fiscal 2015 and thereafter mainly for severance and other closure related costs at the impacted locations.

As of June 30, 2015, Cabot has $4 million of accrued severance and other closure related costs in the Consolidated Balance Sheets related to these activities.

Previous Actions and Sites Pending Sale

Beginning in fiscal 2009, the Company entered into several different restructuring plans which have been substantially completed, pending the sale of former manufacturing sites in Thane, India and Hong Kong. The Company has incurred total cumulative pre-tax charges of approximately $165 million related to these plans through June 30, 2015, comprised of $67 million for severance charges, $66 million for accelerated depreciation and asset impairments, $10 million for environmental, demolition and site clearing costs, and $23 million of other closure related charges, partially offset by gains on asset sales of $1 million. These amounts do not include any gain that may be recorded if the Company successfully sells its land rights and certain manufacturing related assets in India and Hong Kong.

Pre-tax restructuring expenses related to these plans were approximately $2 million and $6 million during the first nine months of fiscal 2015 and 2014, respectively, and less than $1 million in each of the three months ended June 30, 2015 and 2014, respectively. Since fiscal 2009, Cabot has made net cash payments of $86 million related to these plans and expects to pay approximately $3 million in the remainder of fiscal 2015 and thereafter. The remaining payments consist mainly of environmental and other closure related costs.

As of June 30, 2015, Cabot has $2 million of accrued environmental, severance and other closure related costs in the Consolidated Balance Sheets related to these activities.

Financial Instruments and Fair Value Measurements

9 Months Ended

Jun. 30, 2015

Fair Value Disclosures [Abstract]

Financial Instruments and Fair Value Measurements

N. Financial Instruments and Fair Value Measurements

The FASB authoritative guidance on fair value measurements defines fair value, provides a framework for measuring fair value in generally accepted accounting principles, and requires certain disclosures about fair value measurements. The 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, or transfers into or out of Level 3, during the first nine months of either fiscal 2015 or 2014.

At June 30, 2015 and September 30, 2014, the fair value of guaranteed investment contracts, included in Other assets in the Consolidated Balance Sheets, was $12 million and $13 million, respectively, which approximated their carrying values in both periods. 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 June 30, 2015 and September 30, 2014, the fair values of cash and cash equivalents, accounts and notes receivable, accounts payable and accrued liabilities, and notes payable and variable rate debt approximated their carrying values due to the short-term nature of these instruments. The carrying values and fair values of the long-term fixed rate debt were $0.96 billion and $1.01 billion, respectively, as of June 30, 2015 and $0.98 billion and $1.05 billion, respectively, as of September 30, 2014. The fair values of Cabot’s fixed rate long-term debt and capital lease obligations 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.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Derivatives

9 Months Ended

Jun. 30, 2015

Derivative Instruments And Hedging Activities Disclosure [Abstract]

Derivatives

O. Derivatives

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 June 30, 2015 and September 30, 2014, there were no derivatives held to manage interest 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 a currency where the Company expects long-term, stable cash receipts.

Additionally, the Company has foreign currency exposure arising from its net investments in foreign operations. Cabot, from time to time, enters 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 June 30, 2015 and September 30, 2014 to manage foreign currency risk.

Notional Amount, net

Description

Borrowing

June 30, 2015

September 30, 2014

Hedge Designation

Forward Foreign Currency Contracts ⁽¹⁾

N/A

USD 1 million

USD 32 million

No designation

⁽¹⁾	Cabot’s forward foreign exchange contracts are denominated primarily in the Brazilian real, British pound sterling, Czech koruna, Indonesian rupiah, and Mexican peso.

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 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. 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.

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 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.

For both June 30, 2015 and September 30, 2014, the fair value of derivative instruments were immaterial and were presented in Prepaid expenses and other current assets and Accounts payable and accrued liabilities on the Consolidated Balance Sheets.

The net after-tax amounts to be reclassified from AOCI to earnings within the next 12 months are expected to be immaterial.

- Definition

The entire disclosure for derivative instruments and hedging activities including, but not limited to, risk management strategies, non-hedging derivative instruments, assets, liabilities, revenue and expenses, and methodologies and assumptions used in determining the amounts.

+ References

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+ Details

Venezuela	9 Months Ended
Venezuela	Jun. 30, 2015
Equity Method Investments And Joint Ventures [Abstract]
Venezuela	P. Venezuela Cabot owns 49% of an operating carbon black affiliate in Venezuela, which is accounted for as an equity affiliate, through wholly-owned subsidiaries that carry the investment and receive its dividends. As of June 30, 2015, these subsidiaries carried the operating affiliate investment of $15 million and held 18 million bolivars (less than $1 million) in cash. During each of the nine months ended June 30, 2015 and 2014, the operating affiliate declared a dividend in the amount of $5 million and $4 million, respectively, which were paid in U.S. dollars and repatriated to the Company’s wholly-owned subsidiaries. A significant portion of the Company’s operating affiliate’s sales are exports denominated in U.S. dollars. The Venezuelan government mandates that a certain percentage of the dollars collected from these sales be converted into bolivars. The operating affiliate and the Company’s wholly owned subsidiaries used an exchange rate that is available to the Company when converting these dollars into bolivars to remeasure their bolivar denominated monetary accounts. The exchange rate made available to the Company on June 30, 2015 was 52 bolivars to the U.S. dollar (B/$). The operating entity has generally been profitable. The Company continues to closely monitor developments in Venezuela and their potential impact on the recoverability of its equity affiliate investment. The Company closely monitors its ability to convert its bolivar holdings into U.S. dollars, as the Company intends to convert substantially all bolivars held by its wholly-owned subsidiaries in Venezuela to U.S. dollars as soon as practical. Any future change in the exchange rate made available to the Company or opening of additional parallel markets could cause the Company to change the exchange rate it uses and result in gains or losses on the bolivar denominated assets held by its operating affiliate and wholly-owned subsidiaries.

Financial Information by Segment

9 Months Ended

Jun. 30, 2015

Segment Reporting [Abstract]

Financial Information by Segment

Q. Financial Information by Segment

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”) 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 reported 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 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.

In December 2014, the Company realigned its business reporting structure into four segments that consist of Reinforcement Materials, Performance Chemicals, Purification Solutions and Specialty Fluids. Segment results have been recast for all periods presented to reflect the realignment of the Company’s global business segments. The new segment structure is designed to improve efficiency and resource prioritization and reflects how the Company’s CODM reviews segment results to assess performance and allocate resources.

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

The Performance Chemicals segment combines the specialty carbons and compounds and inkjet colorants product lines into the Specialty Carbons and Formulations business, and combines the fumed metal oxides and aerogel product lines into the Metal Oxides 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 includes cesium formate oil and gas drilling fluids and high-purity fine cesium chemicals product lines.

Reportable segment operating profit (loss) before interest and taxes (“Segment EBIT”) is presented for each reportable segment in the financial information by 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 segment results. In addition, Segment EBIT includes Equity in earnings (loss) of affiliated companies, net of tax, the full operating results of a contractual joint venture in Purification Solutions, royalties, Net income 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, the effects of LIFO accounting for inventory, general unallocated expense and unallocated corporate costs.

Financial information by reportable segment is as follows:

	Reinforcement Materials		Performance Chemicals		Purification Solutions			Specialty Fluids		Segment Total		Unallocated and Other⁽¹⁾			Consolidated Total
	(Dollars in millions)
Three Months Ended June 30, 2015
Revenues from external customers⁽²⁾	$	351	$	234	$	72		$	12	$	669	$	25		$	694
Income (loss) from continuing operations before taxes⁽³⁾	$	32	$	48	$	3		$	3	$	86	$	(595	)	$	(509	)

Three Months Ended June 30, 2014
Revenues from external customers⁽²⁾	$	538	$	262	$	78		$	24	$	902	$	38		$	940
Income (loss) from continuing operations before taxes⁽³⁾	$	62	$	44	$	(7	)	$	10	$	109	$	(29	)	$	80

Nine Months Ended June 30, 2015
Revenues from external customers⁽²⁾	$	1,169	$	700	$	219		$	36	$	2,124	$	76		$	2,200
Income (loss) from continuing operations before taxes⁽³⁾	$	112	$	129	$	3		$	8	$	252	$	(671	)	$	(419	)

Nine Months Ended June 30, 2014
Revenues from external customers⁽²⁾	$	1,583	$	763	$	230		$	77	$	2,653	$	83		$	2,736
Income (loss) from continuing operations before taxes⁽³⁾	$	200	$	127	$	(20	)	$	32	$	339	$	(102	)	$	237

⁽¹⁾	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 Chief Operating Decision Maker.

⁽²⁾

Unallocated and Other revenues from external customers reflects royalties, other operating revenues, external shipping and handling costs, 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:

	Three Months Ended June 30					Nine Months Ended June 30
	2015			2014		2015			2014
	(Dollars in millions)
Royalties, other operating revenues, the impact of unearned revenue, the removal of 100% of the sales of an equity method affiliate and discounting charges for certain Notes receivable.	$	(5	)	$	10	$	(9	)	$	(2	)
Shipping and handling fees		30			28		85			85
Total	$	25		$	38	$	76		$	83

⁽³⁾	Income (loss) from continuing operations before taxes that are categorized as Unallocated and Other includes:

	Three Months Ended June 30						Nine Months Ended June 30
	2015			2014			2015			2014
	(Dollars in millions)
Interest expense	$	(13	)	$	(14	)	$	(40	)	$	(41	)
Total certain items, pre-tax^(a)		(567	)		(7	)		(599	)		(19	)
Equity in (earnings) loss of affiliated companies, net of tax^(b)		(1	)		2			(4	)		2
Unallocated corporate costs^(c)		(12	)		(14	)		(35	)		(43	)
General unallocated income (expense)^(d)		(2	)		4			7			(1	)
Total	$	(595	)	$	(29	)	$	(671	)	$	(102	)

^(a)

Certain items are items that management does not consider to be representative of operating segment results and they are, therefore, excluded from Segment EBIT. Certain items, pre-tax, for the three months ended June 30, 2015 include $563 million related to goodwill and long-lived asset impairment charges for the Purification Solutions business, $2 million related to global restructuring activities, and $2 million related to foreign currency loss on revaluations. Certain items, pre-tax, for the nine months ended June 30, 2015 include $563 million related to goodwill and long-lived asset impairment charges for the Purification Solutions business, $14 million related to global restructuring activities, $2 million for acquisition and integration-related charges, $18 million related to an employee benefit plan settlement charge, and $2 million related to foreign currency loss on revaluations. Certain items, pre-tax, for the three months ended June 30, 2014 include $3 million related to global restructuring activities, $3 million of foreign currency loss on revaluations and $1 million for legal and environmental matters and reserves. Certain items, pre-tax, for the nine months ended June 30, 2014 include $24 million related to global restructuring activities, $5 million for acquisition and integration-related charges (consisting of $3 million for certain other one-time integration costs and $2 million of additional charges related to acquisition accounting adjustments for the acquired inventory of NHUMO), $3 million of foreign currency loss on revaluations and $16 million for legal and environmental matters and reserves offset by a $29 million non-cash gain recognized on the Company’s pre-existing investment in NHUMO as a result of the NHUMO transaction.

^(b)	Equity in (earnings) loss 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.

^(c)	Unallocated corporate costs are not controlled by the segments and primarily benefit corporate interests.

^(d)

General unallocated income consists of gains (losses) arising from foreign currency transactions, net of other foreign currency risk management activities, the impact of accounting for certain inventory on a LIFO basis, the profit or loss related to the corporate adjustment for unearned revenue, and the impact of including the full operating results of an equity affiliate in Purification Solutions Segment EBIT.

Performance Chemicals is comprised of two businesses that sell the following products: specialty grades of carbon black, thermoplastic concentrates and compounds and inkjet colorants (the Specialty Carbons and Formulation business); and fumed silica, fumed alumina and dispersions thereof, and aerogel (the Metal Oxides business). The net sales from each of these businesses for the three and nine months ended June 30, 2015 and 2014 are as follows:

	Three Months Ended June 30				Nine Months Ended June 30
	2015		2014		2015		2014
	(Dollars in millions)
Specialty Carbons and Formulations	$	159	$	182	$	478	$	531
Metal Oxides		75		80		222		232
Total Performance Chemicals	$	234	$	262	$	700	$	763

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

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-Name Accounting Standards Codification
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+ Details

Significant Accounting Policies (Policies)

9 Months Ended

Jun. 30, 2015

Accounting Policies [Abstract]

Revenue Recognition and Accounts Receivable

Shipping and handling charges related to sales transactions are recorded as sales revenue when billed to customers or included in the sales price.

The following table shows the relative size of the revenue recognized in each of the Company’s reportable segments for the periods presented.

	Three Months Ended June 30						Nine Months Ended June 30
	2015			2014			2015			2014
Reinforcement Materials		52	%		60	%		55	%		59	%
Performance Chemicals		35	%		29	%		33	%		29	%
Purification Solutions		11	%		9	%		10	%		9	%
Specialty Fluids		2	%		2	%		2	%		3	%

Intangible Assets and Goodwill Impairment

Long-lived Assets Impairment

Property, Plant and Equipment

Income Tax in Interim Periods

Inventory Valuation

Pensions and Other Postretirement Benefits

Accumulated Other Comprehensive (Loss) Income

Recent Accounting Pronouncements

Significant Accounting Policies (Tables)

9 Months Ended

Jun. 30, 2015

Accounting Policies [Abstract]

Segment Reporting Revenue Percentage

The following table shows the relative size of the revenue recognized in each of the Company’s reportable segments for the periods presented.

	Three Months Ended June 30						Nine Months Ended June 30
	2015			2014			2015			2014
Reinforcement Materials		52	%		60	%		55	%		59	%
Performance Chemicals		35	%		29	%		33	%		29	%
Purification Solutions		11	%		9	%		10	%		9	%
Specialty Fluids		2	%		2	%		2	%		3	%

Acquisition of NHUMO (Tables)

9 Months Ended

Jun. 30, 2015

Business Combinations [Abstract]

Components and Allocation of Purchase Price

The following table presents the components and allocation of the purchase price:

	(Dollars in millions)
Assets
Current assets	$	54
Property, plant and equipment		48
Other non-current assets		1
Intangible assets		63
Goodwill		45
Total assets acquired		211
Liabilities
Accounts payable, accruals and other liabilities		(20	)
Deferred tax liabilities - long-term		(29	)
Total liabilities assumed		(49	)
Net assets acquired	$	162
Cash consideration paid		80
Fair value of redeemable preferred stock		28
Previously held equity interest in NHUMO		54
Total	$	162

Employee Benefit Plans (Tables)

9 Months Ended

Jun. 30, 2015

Compensation And Retirement Disclosure [Abstract]

Net Periodic Defined Benefit Pension and Other Postretirement Benefit Costs

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

	Three Months Ended June 30
	2015						2014						2015					2014
	Pension Benefits												Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign		U.S.			Foreign
	(Dollars in millions)
Service cost	$	—		$	2		$	1		$	2		$	—		$	—	$	—		$	—
Interest cost		2			3			2			4			—			1		1			1
Expected return on plan assets		(3	)		(4	)		(3	)		(5	)		—			—		—			—
Amortization of prior service credit		—			—			—			—			(1	)		—		(1	)		—
Amortization of actuarial loss		—			1			—			1			—			—		—			—
Net periodic benefit (credit) cost	$	(1	)	$	2		$	—		$	2		$	(1	)	$	1	$	—		$	1

	Nine Months Ended June 30
	2015						2014						2015					2014
	Pension Benefits												Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign		U.S.			Foreign
	(Dollars in millions)
Service cost	$	—		$	7		$	2		$	7		$	—		$	—	$	—		$	—
Interest cost		5			9			6			12			1			1		2			1
Expected return on plan assets		(8	)		(12	)		(8	)		(15	)		—			—		—			—
Amortization of prior service credit		—			—			—			—			(2	)		—		(2	)		—
Amortization of actuarial loss		—			3			—			3			—			—		—			—
Settlement costs		—			18			—			—			—			—		—			—
Net periodic benefit (credit) cost	$	(3	)	$	25		$	—		$	7		$	(1	)	$	1	$	—		$	1

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

9 Months Ended

Jun. 30, 2015

Goodwill And Intangible Assets Disclosure [Abstract]

Impairment Charges and Associated Tax Benefit

	June 30, 2015
		(Dollars in millions)
Goodwill impairment charge	$	353
Long-lived assets impairment charge		209
Provision (benefit) for income taxes		(80	)
Impairment charges, after tax	$	482

Goodwill and Intangible Assets (Tables)

9 Months Ended

Jun. 30, 2015

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 June 30, 2015 are as follows:

	Reinforcement Materials			Performance Chemicals			Purification Solutions			Total
	(Dollars in millions)
Balance at September 30, 2014	$	68		$	10		$	458		$	536
Impairment charge		—			—			(353	)		(353	)
Foreign currency impact		(9	)		(1	)		(16	)		(26	)
Balance at June 30, 2015	$	59		$	9		$	89		$	157

Schedule of Intangible Assets

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

	June 30, 2015							September 30, 2014
	Gross Carrying Value		Accumulated Amortization			Net Intangible Assets		Gross Carrying Value		Accumulated Amortization			Net Intangible Assets
	(Dollars in millions)
Intangible assets with finite lives⁽¹⁾
Developed technologies	$	48	$	—		$	48	$	152	$	(16	)	$	136
Trademarks		16		—			16		57		—			57
Customer relationships		100		(5	)		95		171		(17	)		154
Total intangible assets	$	164	$	(5	)	$	159	$	380	$	(33	)	$	347

Stockholders' Equity (Tables)

9 Months Ended

Jun. 30, 2015

Equity [Abstract]

Schedule of Activity in Noncontrolling Interests

The following table illustrates the noncontrolling interest activity for the periods presented:

	2015			2014
	(Dollars in millions)
Balance at September 30	$	122		$	132
Net income attributable to noncontrolling interest		7			14
Noncontrolling interest foreign currency translation adjustment		(3	)		(2	)
Noncontrolling interest dividends		(22	)		(25	)
Balance at June 30	$	104		$	119

Accumulated Other Comprehensive Loss (Tables)

9 Months Ended

Jun. 30, 2015

Equity [Abstract]

Changes in Each Component of AOCI, Net of Tax

Changes in each component of AOCI, net of tax, are as follows:

						Pension and Other
	Currency			Unrealized		Postretirement
	Translation			Gains on		Benefit Liability
	Adjustment			Investments		Adjustments			Total
	(Dollars in millions)
Balance at September 30, 2014, attributable to Cabot Corporation	$	27		$	2	$	(93	)	$	(64	)
Other comprehensive loss before reclassifications		(103	)		—		—			(103	)
Amounts reclassified from accumulated other comprehensive income		—			—		21			21
Net other comprehensive items		(103	)		—		21			(82	)
Less: Noncontrolling interest		(2	)		—		—			(2	)
Balance at December 31, 2014, attributable to Cabot Corporation	$	(74	)	$	2	$	(72	)	$	(144	)
Other comprehensive loss before reclassifications		(131	)		—		—			(131	)
Amounts reclassified from accumulated other comprehensive income		—			—		1			1
Net other comprehensive items		(131	)		—		1			(130	)
Less: Noncontrolling interest		(1	)		—		—			(1	)
Balance at March 31, 2015, attributable to Cabot Corporation	$	(204	)	$	2	$	(71	)	$	(273	)
Other comprehensive income before reclassifications		18			—		—			18
Amounts reclassified from accumulated other comprehensive income		—			—		—			—
Net other comprehensive items		18			—		—			18
Less: Noncontrolling interest		—			—		—			—
Balance at June 30, 2015, attributable to Cabot Corporation	$	(186	)	$	2	$	(71	)	$	(255	)

Accumulated Other Comprehensive Items in Accompanying Consolidated Balance Sheets

Accumulated other comprehensive items in the accompanying Consolidated Balance Sheets consist of the following items, net of tax:

	June 30,			September 30,
	2015			2014
	(Dollars in millions)
Foreign currency translation adjustments at beginning of period	$	27		$	154
Net foreign currency translation adjustments attributable to Cabot during the period		(213	)		(127	)
Balance at end of period		(186	)		27
Unrealized gain on investments at beginning of period		2			2
Net unrealized gains during the period		—			—
Balance at end of period		2			2
Pension and other postretirement benefit plans attributable to Cabot at beginning of period		(93	)		(53	)
Net change in pension and other postretirement benefit plans during the period		22			(40	)
Balance at end of period		(71	)		(93	)
Total accumulated other comprehensive loss	$	(255	)	$	(64	)

Amounts Reclassified Out of AOCI

The amounts reclassified out of AOCI and into the Consolidated Statements of Operations for the three and nine months ended June 30, 2015 and 2014 are as follows:

		Three Months Ended						Nine Months Ended
	Affected Line Item in the Consolidated	June 30,						June 30,
	Statements of Operations	2015			2014			2015			2014
		(Dollars in millions)
Pension and other postretirement benefit liability adjustment
Amortization of actuarial losses	Net Periodic Benefit Cost - see Note E for details	$	1		$	1		$	3		$	3
Amortization of prior service cost	Net Periodic Benefit Cost - see Note E for details		(1	)		(1	)		(2	)		(2	)
Settlement costs	Net Periodic Benefit Cost - see Note E for details		—			—			27			—
Total before tax			—			—			28			1
Tax impact	Benefit for income taxes		—			—			(6	)		—
Total after tax		$	—		$	—		$	22		$	1

Commitments and Contingencies (Tables)

9 Months Ended

Jun. 30, 2015

Commitments And Contingencies Disclosure [Abstract]

Schedule of Components of Purchase Commitments

	Payments Due by Fiscal Year
	Remainder of Fiscal 2015		2016		2017		2018		2019		Thereafter		Total
	(Dollars in millions)
Reinforcement Materials	$	86	$	227	$	178	$	177	$	173	$	1,911	$	2,752
Performance Chemicals		19		60		38		33		33		210		393
Purification Solutions		7		13		9		7		7		8		51
Total	$	112	$	300	$	225	$	217	$	213	$	2,129	$	3,196

Income Tax (Tables)

9 Months Ended

Jun. 30, 2015

Income Tax Disclosure [Abstract]

Effective Tax Rate

	Three Months Ended June 30						Nine Months Ended June 30
	2015			2014			2015			2014
	(Dollars in millions)						(Dollars in millions)
(Benefit) Provision for income taxes	$	(64	)	$	20		$	(47	)	$	51
Effective tax rate		13	%		25	%		11	%		22	%

Earnings Per Share (Tables)

9 Months Ended

Jun. 30, 2015

Earnings Per Share [Abstract]

Components of Basic and Diluted Earnings Per Common Share

The following tables summarize the components of the basic and diluted earnings per common share computations:

	Three Months Ended June 30						Nine Months Ended June 30
	2015			2014			2015			2014
	(Dollars and shares in millions, except per share amounts)
Basic EPS:
Net (loss) income attributable to Cabot Corporation	$	(445	)	$	52		$	(374	)	$	168
Less: Dividends and dividend equivalents to participating securities		—			—			—			—
Less: Undistributed earnings allocated to participating securities⁽¹⁾		—			1			—			2
(Loss) earnings allocated to common shareholders (numerator)	$	(445	)	$	51		$	(374	)	$	166
Weighted average common shares and participating securities outstanding		63.8			65.1			64.2			64.9
Less: Participating securities⁽¹⁾		0.5			0.6			0.5			0.6
Adjusted weighted average common shares (denominator)		63.3			64.5			63.7			64.3
Amounts per share - basic:
(Loss) income from continuing operations attributable to Cabot Corporation	$	(7.05	)	$	0.80		$	(5.89	)	$	2.61
Income (loss) from discontinued operations		0.01			(0.01	)		0.01			(0.03	)
Net (loss) income attributable to Cabot Corporation	$	(7.04	)	$	0.79		$	(5.88	)	$	2.58
Diluted EPS⁽²⁾:
(Loss) earnings allocated to common shareholders	$	(445	)	$	51		$	(374	)	$	166
Plus: (Loss) earnings allocated to participating securities		—			1			—			2
Less: Adjusted earnings allocated to participating securities⁽³⁾		—			(1	)		—			(2	)
(Loss) earnings allocated to common shareholders (numerator)	$	(445	)	$	51		$	(374	)	$	166
Adjusted weighted average common shares outstanding		63.3			64.5			63.7			64.3
Effect of dilutive securities:
Common shares issuable⁽⁴⁾		—			0.7			—			0.7
Adjusted weighted average common shares (denominator)		63.3			65.2			63.7			65.0
Amounts per share - diluted:
(Loss) income from continuing operations attributable to Cabot Corporation	$	(7.05	)	$	0.79		$	(5.89	)	$	2.58
Income (loss) from discontinued operations		0.01			(0.01	)		0.01			(0.03	)
Net (loss) income attributable to Cabot Corporation	$	(7.04	)	$	0.78		$	(5.88	)	$	2.55

⁽¹⁾	Participating securities consist of shares of unvested restricted stock and unvested time-based restricted stock units.

Calculation of Undistributed Earnings

	Three Months Ended June 30					Nine Months Ended June 30
	2015			2014		2015			2014
	(Dollars in millions)
Calculation of undistributed (loss) earnings:
Net (loss) income attributable to Cabot Corporation	$	(445	)	$	52	$	(374	)	$	168
Less: Dividends declared on common stock		14			14		42			40
Less: Dividends declared on participating securities		—			—		—			—
Undistributed (loss) earnings	$	(459	)	$	38	$	(416	)	$	128
Allocation of undistributed (loss) earnings:
Undistributed (loss) earnings allocated to common shareholders	$	(459	)	$	37	$	(416	)	$	126
Undistributed (loss) earnings allocated to participating shareholders		—			1		—			2
Undistributed (loss) earnings	$	(459	)	$	38	$	(416	)	$	128

⁽²⁾	Due to the Company’s net loss position, dividends on participating securities were not added back to loss available to common shares for the three and nine months ended June 30, 2015 when calculating diluted EPS.

⁽³⁾	Undistributed earnings are adjusted for the assumed distribution of dividends to the dilutive securities, which are described in (4) below, and then reallocated to participating securities.

⁽⁴⁾

Restructuring (Tables)

9 Months Ended

Jun. 30, 2015

Restructuring And Related Activities [Abstract]

Recorded Restructuring Activities

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

	Three Months Ended June 30				Nine Months Ended June 30
	2015		2014		2015		2014
	(Dollars in millions)
Cost of sales	$	1	$	2	$	4	$	11
Selling and administrative expenses		1		2		10		13
Total	$	2	$	4	$	14	$	24

Restructuring Activities and Related Reserves

Details of these restructuring activities and the related reserves during the three months ended June 30, 2015 are as follows:

	Severance and Employee Benefits			Environmental Remediation		Other		Total
	(Dollars in millions)
Reserve at March 31, 2015	$	9		$	3	$	1	$	13
Charges		2			—		—		2
Cash paid		(5	)		—		—		(5	)
Reserve at June 30, 2015	$	6		$	3	$	1	$	10

Details of these restructuring activities and the related reserves during the nine months ended June 30, 2015 are as follows:

	Severance and Employee Benefits			Environmental Remediation		Asset Impairment and Accelerated Depreciation			Other			Total
	(Dollars in millions)
Reserve at September 30, 2014	$	16		$	2	$	—		$	1		$	19
Charges		7			1		1			5			14
Costs charged against assets / liabilities		—			—		(1	)		—			(1	)
Cash paid		(15	)		—		—			(5	)		(20	)
Foreign currency translation adjustment		(2	)		—		—			—			(2	)
Reserve at June 30, 2015	$	6		$	3	$	—		$	1		$	10

Derivatives (Tables)

9 Months Ended

Jun. 30, 2015

Forward Foreign Currency Contracts [Member]

Schedule of Derivatives Foreign Currency

The following table provides details of the derivatives held as of June 30, 2015 and September 30, 2014 to manage foreign currency risk.

Notional Amount, net

Description

Borrowing

June 30, 2015

September 30, 2014

Hedge Designation

Forward Foreign Currency Contracts ⁽¹⁾

N/A

USD 1 million

USD 32 million

No designation

⁽¹⁾	Cabot’s forward foreign exchange contracts are denominated primarily in the Brazilian real, British pound sterling, Czech koruna, Indonesian rupiah, and Mexican peso.

- 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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=56946850&loc=d3e41641-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624163-113959

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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-Paragraph 8
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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-Section 50
-Paragraph 4
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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-Section 50
-Paragraph 1B
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624171-113959

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 25
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6886632&loc=d3e76258-113986

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5579240-113959

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=56946850&loc=d3e41620-113959

Reference 11: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(n)(2))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

Financial Information by Segment (Tables)

9 Months Ended

Jun. 30, 2015

Segment Reporting [Abstract]

Financial Information by Reportable Segment

Financial information by reportable segment is as follows:

	Reinforcement Materials		Performance Chemicals		Purification Solutions			Specialty Fluids		Segment Total		Unallocated and Other⁽¹⁾			Consolidated Total
	(Dollars in millions)
Three Months Ended June 30, 2015
Revenues from external customers⁽²⁾	$	351	$	234	$	72		$	12	$	669	$	25		$	694
Income (loss) from continuing operations before taxes⁽³⁾	$	32	$	48	$	3		$	3	$	86	$	(595	)	$	(509	)

Three Months Ended June 30, 2014
Revenues from external customers⁽²⁾	$	538	$	262	$	78		$	24	$	902	$	38		$	940
Income (loss) from continuing operations before taxes⁽³⁾	$	62	$	44	$	(7	)	$	10	$	109	$	(29	)	$	80

Nine Months Ended June 30, 2015
Revenues from external customers⁽²⁾	$	1,169	$	700	$	219		$	36	$	2,124	$	76		$	2,200
Income (loss) from continuing operations before taxes⁽³⁾	$	112	$	129	$	3		$	8	$	252	$	(671	)	$	(419	)

Nine Months Ended June 30, 2014
Revenues from external customers⁽²⁾	$	1,583	$	763	$	230		$	77	$	2,653	$	83		$	2,736
Income (loss) from continuing operations before taxes⁽³⁾	$	200	$	127	$	(20	)	$	32	$	339	$	(102	)	$	237

⁽¹⁾	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 Chief Operating Decision Maker.

⁽²⁾

	Three Months Ended June 30					Nine Months Ended June 30
	2015			2014		2015			2014
	(Dollars in millions)
Royalties, other operating revenues, the impact of unearned revenue, the removal of 100% of the sales of an equity method affiliate and discounting charges for certain Notes receivable.	$	(5	)	$	10	$	(9	)	$	(2	)
Shipping and handling fees		30			28		85			85
Total	$	25		$	38	$	76		$	83

⁽³⁾	Income (loss) from continuing operations before taxes that are categorized as Unallocated and Other includes:

	Three Months Ended June 30						Nine Months Ended June 30
	2015			2014			2015			2014
	(Dollars in millions)
Interest expense	$	(13	)	$	(14	)	$	(40	)	$	(41	)
Total certain items, pre-tax^(a)		(567	)		(7	)		(599	)		(19	)
Equity in (earnings) loss of affiliated companies, net of tax^(b)		(1	)		2			(4	)		2
Unallocated corporate costs^(c)		(12	)		(14	)		(35	)		(43	)
General unallocated income (expense)^(d)		(2	)		4			7			(1	)
Total	$	(595	)	$	(29	)	$	(671	)	$	(102	)

^(a)

^(b)	Equity in (earnings) loss 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.

^(c)	Unallocated corporate costs are not controlled by the segments and primarily benefit corporate interests.

^(d)

Schedule of Performance Segment

The net sales from each of these businesses for the three and nine months ended June 30, 2015 and 2014 are as follows:

	Three Months Ended June 30				Nine Months Ended June 30
	2015		2014		2015		2014
	(Dollars in millions)
Specialty Carbons and Formulations	$	159	$	182	$	478	$	531
Metal Oxides		75		80		222		232
Total Performance Chemicals	$	234	$	262	$	700	$	763

Basis of Presentation - Additional Information (Detail)	1 Months Ended
Basis of Presentation - Additional Information (Detail)	Dec. 31, 2014 Segments	Dec. 31, 2014 Segment	Nov. 30, 2013
Basis Of Presentation [Line Items]
Number of reporting segments	4	4
NHUMO [Member]
Basis Of Presentation [Line Items]
Percentage acquisition			60.00%
Ownership percentage prior to acquisition			40.00%

Significant Accounting Policies - Segment Reporting Revenue Percentage (Detail) - Sales Revenue, Segment [Member] - Segment Concentration Risk [Member]	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	52.00%	60.00%	55.00%	59.00%
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	35.00%	29.00%	33.00%	29.00%
Purification Solutions [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	11.00%	9.00%	10.00%	9.00%
Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Revenue, by segment	2.00%	2.00%	2.00%	3.00%

Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2015	Sep. 30, 2014
Significant Accounting Policies [Line Items]
Value of inventories under FIFO method	$ 37	$ 52
Buildings [Member] \| Minimum [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment	20 years
Buildings [Member] \| Maximum [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment	25 years
Machinery and Equipment [Member] \| Minimum [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment	10 years
Machinery and Equipment [Member] \| Maximum [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment	25 years
Other Fixed Assets [Member] \| Minimum [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment	3 years
Other Fixed Assets [Member] \| Maximum [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment	25 years

Acquisition of NHUMO - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended		9 Months Ended
	Sep. 30, 2014	Nov. 30, 2013	Jun. 30, 2015	Jun. 30, 2014
Business Acquisition [Line Items]
Preferred stock redemption amount	$ 27.0		$ 28.0
Gain on acquisition				$ 29.0
Customer Relationships [Member]
Business Acquisition [Line Items]
Intangible asset			$ 63.0
Amortized period			20 years
NHUMO [Member]
Business Acquisition [Line Items]
Percentage acquisition		60.00%
Ownership percentage prior to acquisition		40.00%
Cash paid on acquisition	80.0	$ 80.0
Dividend percentage of preferred stock		6.00%
Preferred stock issued on acquisition		$ 25.0
Dividend payment		1.5
Dividend received from NHUMO		14.0
Gain on acquisition			$ 29.0
Previously held equity interest in NHUMO	$ 54.0		$ 54.0
NHUMO [Member] \| Carrying Value [Member]
Business Acquisition [Line Items]
Preferred stock redemption amount		$ 25.0

Acquisition of NHUMO - Components and Allocation of Purchase Price (Detail) - USD ($) $ in Millions	1 Months Ended		9 Months Ended
	Sep. 30, 2014	Nov. 30, 2013	Jun. 30, 2015
Assets
Goodwill	$ 536		$ 157
NHUMO [Member]
Assets
Current assets	54
Property, plant and equipment	48
Other non-current assets	1
Intangible assets	63
Goodwill	45
Total assets acquired	211
Liabilities
Accounts payable, accruals and other liabilities	(20)
Deferred tax liabilities - long-term	(29)
Total liabilities assumed	(49)
Net assets acquired	162
Cash consideration paid	80	$ 80
Fair value of redeemable preferred stock	28
Previously held equity interest in NHUMO	54		$ 54
Total	$ 162

Discontinued Operations - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Discontinued Operations And Disposal Groups [Abstract]
Income (loss) from discontinued operations, net of tax	$ 1	$ (1)	$ 1	$ (2)

- Definition

Amount after tax of income (loss) from a discontinued operation including the portion attributable to the noncontrolling interest. Includes, but is not limited to, the income (loss) from operations during the phase-out period, gain (loss) on disposal, gain (loss) for reversal of write-down (write-down) to fair value, less cost to sell, and adjustments to a prior period gain (loss) on disposal.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.12)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5C
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=51717284&loc=SL51721675-107760

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.14)
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=51716988&loc=d3e1012-107759

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 3B
-URI http://asc.fasb.org/extlink&oid=51716988&loc=SL51721525-107759

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 3A
-URI http://asc.fasb.org/extlink&oid=51716988&loc=SL51721523-107759

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=51716988&loc=d3e957-107759

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51717284&loc=d3e1361-107760

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 13
-Article 7

Reference 10: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 15
-Article 5

+ Details

Employee Benefit Plans - Net Periodic Defined Benefit Pension and Other Postretirement Benefit Costs (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Settlement costs			$ 18
U.S. Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost		$ 1		$ 2
Interest cost	$ 2	2	5	6
Expected return on plan assets	(3)	(3)	(8)	(8)
Net periodic benefit (credit) cost	(1)		(3)
Foreign Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	2	7	7
Interest cost	3	4	9	12
Expected return on plan assets	(4)	(5)	(12)	(15)
Amortization of actuarial loss	1	1	3	3
Settlement costs			18
Net periodic benefit (credit) cost	2	2	25	7
United States Postretirement Benefit Plans Of U S Entity Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Interest cost		1	1	2
Amortization of prior service credit	(1)	(1)	(2)	(2)
Net periodic benefit (credit) cost	(1)		(1)
Foreign Postretirement Benefit Plans Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1	1	1
Net periodic benefit (credit) cost	$ 1	$ 1	$ 1	$ 1

Employee Benefit Plans - Additional Information (Detail) $ in Millions	9 Months Ended
	Jun. 30, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Settlement costs	$ 18
Pre-tax charge from AOCI	27
Settlement charges on pension liability	11
Settlement charges on employer contributions	$ 2
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Contribution to multi-employer plan	80.00%

Purification Solutions Goodwill and Long-Lived Assets Impairment Charges - Impairment Charges and Associated Tax Benefit (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2015	Jun. 30, 2015	Jun. 30, 2014
Intangible Assets [Line Items]
Goodwill impairment charge	$ 353	$ 353
Long-lived asset impairment charge	$ 209	209	$ 4
Deferred tax (benefit) provision		(75)	$ (16)
Impairment charges, after tax		482
Purification Solutions [Member]
Intangible Assets [Line Items]
Goodwill impairment charge		353
Deferred tax (benefit) provision		$ (80)

Purification Solutions Goodwill and Long-Lived Assets Impairment Charges - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2015	Jun. 30, 2015	Jun. 30, 2014
Intangible Assets [Line Items]
Pre-tax goodwill impairment charge	$ 353	$ 353
Impairment loss of indefinite lived Intangibles		39
Impairment charges of definite lived Intangible assets		119
Long-lived asset impairment charge	$ 209	209	$ 4
Deferred tax benefit to income tax provision		75	$ 16
Purification Solutions [Member]
Intangible Assets [Line Items]
Pre-tax goodwill impairment charge		353
Deferred tax benefit to income tax provision		80
Property, Plant and Equipment
Intangible Assets [Line Items]
Long-lived asset impairment charge		$ 51

Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2014
Intangible Assets [Line Items]
Goodwill	$ 157		$ 157		$ 536
Amortization expense estimated for year one	9		9
Amortization expense estimated for year two	9		9
Amortization expense estimated for year three	9		9
Amortization expense estimated for year four	9		9
Amortization expense estimated for year five	9		9
Cost of Sales and Selling and Administrative Expenses [Member]
Intangible Assets [Line Items]
Amortization of intangible assets	$ 3	$ 4	$ 12	$ 13
Minimum [Member]
Intangible Assets [Line Items]
Useful life of intangible assets			14 years
Maximum [Member]
Intangible Assets [Line Items]
Useful life of intangible assets			25 years
Weighted Average [Member]
Intangible Assets [Line Items]
Useful life of intangible assets			19 years

Goodwill and Intangible Assets - Schedule of Goodwill Balances (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2015	Jun. 30, 2015
Goodwill And Other Intangible Asset [Line Items]
Beginning balance		$ 536
Goodwill impairment charge (Note F)	$ (353)	(353)
Foreign currency impact		(26)
Ending balance	157	157
Reinforcement Materials [Member]
Goodwill And Other Intangible Asset [Line Items]
Beginning balance		68
Foreign currency impact		(9)
Ending balance	59	59
Performance Chemicals [Member]
Goodwill And Other Intangible Asset [Line Items]
Beginning balance		10
Foreign currency impact		(1)
Ending balance	9	9
Purification Solutions [Member]
Goodwill And Other Intangible Asset [Line Items]
Beginning balance		458
Goodwill impairment charge (Note F)		(353)
Foreign currency impact		(16)
Ending balance	$ 89	$ 89

Goodwill and Intangible Assets - Schedule of Intangible Assets (Detail) - USD ($) $ in Millions	Jun. 30, 2015	Sep. 30, 2014
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value	$ 164	$ 380
Accumulated Amortization	(5)	(33)
Net Intangible Assets	159	347
Developed Technologies [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	48	152
Accumulated Amortization		(16)
Net Intangible Assets, finite lives	48	136
Trademarks [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	16	57
Net Intangible Assets, finite lives	16	57
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	100	171
Accumulated Amortization	(5)	(17)
Net Intangible Assets, finite lives	$ 95	$ 154

Stockholders' Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jan. 31, 2015	Sep. 30, 2007
Class Of Stock [Line Items]
Repurchase authorization, shares			5,000,000	10,000,000
Cash dividends paid to common stockholders	$ 42	$ 40
Cash dividend paid per share	$ 0.66	$ 0.62
2007 Share Repurchase Authorization [Member]
Class Of Stock [Line Items]
Common stock shares repurchased	925,700	379
January 2015 Share Repurchase Authorization [Member]
Class Of Stock [Line Items]
Common stock shares repurchased	874,300
Shares remaining available for repurchase under the current authorization	4,125,700

Stockholders' Equity - Schedule of Activity in Noncontrolling Interests (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Equity [Abstract]
Balance at September 30			$ 122	$ 132
Net income attributable to noncontrolling interests	$ 2	$ 5	7	14
Noncontrolling interest foreign currency translation adjustment			(3)	(2)
Noncontrolling interest dividends			(22)	(25)
Balance at June 30	$ 104	$ 119	$ 104	$ 119

Accumulated Other Comprehensive Loss - Changes in Each Component of AOCI, Net of Tax (Detail) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Accumulated Other Comprehensive Income Loss [Line Items]
Balance attributable to Cabot Corporation	$ (273)	$ (144)	$ (64)		$ (64)
Other comprehensive loss before reclassifications	18	(131)	(103)
Amounts reclassified from accumulated other comprehensive income		1	21
Other comprehensive income (loss)	18	(130)	(82)	$ 13	(194)	$ (15)
Less: Noncontrolling interest		(1)	(2)
Balance attributable to Cabot Corporation	(255)	(273)	(144)		(255)
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance attributable to Cabot Corporation	(204)	(74)	27		27
Other comprehensive loss before reclassifications	18	(131)	(103)
Other comprehensive income (loss)	18	(131)	(103)
Less: Noncontrolling interest		(1)	(2)
Balance attributable to Cabot Corporation	(186)	(204)	(74)		(186)
Unrealized Gains on Investments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance attributable to Cabot Corporation	2	2	2		2
Balance attributable to Cabot Corporation	2	2	2		2
Pension and Other Postretirement Benefit Liability Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance attributable to Cabot Corporation	(71)	(72)	(93)		(93)
Amounts reclassified from accumulated other comprehensive income		1	21
Other comprehensive income (loss)		1	21
Balance attributable to Cabot Corporation	$ (71)	$ (71)	$ (72)		$ (71)

- Definition

Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

+ References + Details

Accumulated Other Comprehensive Loss - Accumulated Other Comprehensive Items in Accompanying Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Jun. 30, 2015	Sep. 30, 2014	Mar. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Foreign currency translation adjustments at beginning of period	$ 27	$ 154
Net foreign currency translation adjustments attributable to Cabot during the period	(213)	(127)
Foreign currency translation adjustments at end of period	(186)	27
Unrealized gain on investments at beginning of period	2	2
Unrealized gain on investments at end of period	2	2
Pension and other postretirement benefit plans attributable to Cabot at beginning of period	(93)	(53)
Net change in pension and other postretirement benefit plans during the period	22	(40)
Pension and other postretirement benefit plans at end of period	(71)	(93)
Total accumulated other comprehensive loss	$ (255)	$ (64)	$ (273)	$ (144)

- Definition

+ References + Details

Accumulated Other Comprehensive Loss - Amounts Reclassified Out of AOCI (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pre-tax charge from AOCI			$ 27
Total before tax	$ (509)	$ 80	(419)	$ 237
Benefit (provision) for income taxes	64	(20)	47	(51)
(Loss) income from continuing operations	(444)	58	(368)	184
Reclassification Out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Pre-tax charge from AOCI			27
Total before tax			28	1
Benefit (provision) for income taxes			(6)
(Loss) income from continuing operations			22	1
Reclassification Out of Accumulated Other Comprehensive Income [Member] \| Pension and Other Postretirement Benefit Liability Adjustments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amortization of actuarial losses	1	1	3	3
Amortization of prior service cost	$ (1)	$ (1)	$ (2)	$ (2)

Commitments and Contingencies - Additional Information (Detail) $ in Millions	9 Months Ended
	Jun. 30, 2015 USD ($) claimants	Jun. 30, 2014 USD ($)	Sep. 30, 2014 USD ($) claimants
Respirator Liabilities [Member]
Loss Contingencies [Line Items]
Number of claimants \| claimants	38,000		41,000
Respirator reserve on discounted basis	$ 11		$ 13
Cash payments for respirator reserves	2	$ 2
Environmental Matters [Member]
Loss Contingencies [Line Items]
Reserved for environmental matters, on an undiscounted basis	16		$ 17
Cash payments for environmental reserves	$ 1	$ 2

Income Tax - Effective Tax Rate (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Tax Disclosure [Abstract]
(Benefit) Provision for income taxes	$ (64)	$ 20	$ (47)	$ 51
Effective tax rate	13.00%	25.00%	11.00%	22.00%

Income Tax - Additional Information (Detail) $ in Millions	3 Months Ended	9 Months Ended
Income Tax - Additional Information (Detail) $ in Millions	Jun. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)
Income Taxes [Line Items]
Long-lived assets impairment		$ 209
Deferred tax liabilities	$ 80	80
Goodwill impairment charge related to goodwill	353	353
Uncertain tax positions from expirations of statute of limitations	1	13
Deferred tax assets	$ 5	$ 5
Earliest Tax Year [Member] \| U.S. Federal [Member] \| Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Tax years remain subject to examination		2012
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		2004
Latest Tax Year [Member] \| U.S. Federal [Member] \| Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Tax years remain subject to examination		2014
Latest Tax Year [Member] \| State Tax Authorities [Member]
Income Taxes [Line Items]
Tax years remain subject to examination		2014
Latest Tax Year [Member] \| Non-U.S. Jurisdictions [Member]
Income Taxes [Line Items]
Tax years remain subject to examination		2014

Earnings Per Share - Components of Basic and Diluted Earnings Per Common Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Basic EPS:
Net (loss) income attributable to Cabot Corporation	$ (445)	$ 52	$ (374)	$ 168
Less: Undistributed earnings allocated to participating securities		1		2
(Loss) earnings allocated to common shareholders (numerator)	$ (445)	$ 51	$ (374)	$ 166
Weighted average common shares and participating securities outstanding	63.8	65.1	64.2	64.9
Less: Participating securities	0.5	0.6	0.5	0.6
Adjusted weighted average common shares (denominator)	63.3	64.5	63.7	64.3
(Loss) income from continuing operations attributable to Cabot Corporation	$ (7.05)	$ 0.80	$ (5.89)	$ 2.61
Income (loss) from discontinued operations	0.01	(0.01)	0.01	(0.03)
Net (loss) income attributable to Cabot Corporation	$ (7.04)	$ 0.79	$ (5.88)	$ 2.58
Diluted EPS(2):
(Loss) earnings allocated to common shareholders	$ (445)	$ 51	$ (374)	$ 166
Plus: (Loss) earnings allocated to participating securities		1		2
Less: Adjusted earnings allocated to participating securities		(1)		(2)
(Loss) earnings allocated to common shareholders (numerator)	$ (445)	$ 51	$ (374)	$ 166
Adjusted weighted average common shares outstanding	63.3	64.5	63.7	64.3
Common shares issuable		0.7		0.7
Adjusted weighted average common shares (denominator)	63.3	65.2	63.7	65.0
(Loss) income from continuing operations attributable to Cabot Corporation	$ (7.05)	$ 0.79	$ (5.89)	$ 2.58
Income (loss) from discontinued operations	0.01	(0.01)	0.01	(0.03)
Net (loss) income attributable to Cabot Corporation	$ (7.04)	$ 0.78	$ (5.88)	$ 2.55

Earnings Per Share - Calculation of Undistributed Earnings (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Net (loss) income attributable to Cabot Corporation	$ (445)	$ 52	$ (374)	$ 168
Less: Dividends declared on common stock	14	14	42	40
Undistributed (loss) earnings	(459)	38	(416)	128
Undistributed (loss) earnings allocated to common shareholders	$ (459)	37	$ (416)	126
Undistributed (loss) earnings allocated to participating shareholders		$ 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 - Calculation of Undistributed Earnings (Parenthetical) (Detail) - shares	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share	492,172	142,115	508,991	203,019

Restructuring - Recorded Restructuring Activities (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Restructuring Cost and Reserve [Line Items]
Restructuring reserve, period expense	$ 2	$ 4	$ 14	$ 24
Cost of Sales [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring reserve, period expense	1	2	4	11
Selling and Administrative Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring reserve, period expense	$ 1	$ 2	$ 10	$ 13

Restructuring - Restructuring Activities and Related Reserves (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		13 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015
Restructuring Cost and Reserve [Line Items]
Reserve balance	$ 13		$ 19
Charges	2	$ 4	14	$ 24
Costs charged against assets / liabilities			(1)
Cash paid	(5)		(20)		$ (19)
Foreign currency translation adjustment			(2)
Reserve balance	10		10		10
Severance and Employee Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Reserve balance	9		16
Charges	2		7
Cash paid	(5)		(15)
Foreign currency translation adjustment			(2)
Reserve balance	6		6		6
Environmental Remediation [Member]
Restructuring Cost and Reserve [Line Items]
Reserve balance	3		2
Charges			1
Reserve balance	3		3		3
Asset Impairment and Accelerated Depreciation [Member]
Restructuring Cost and Reserve [Line Items]
Charges			1
Costs charged against assets / liabilities			(1)
Other [Member]
Restructuring Cost and Reserve [Line Items]
Reserve balance	1		1
Charges			5
Cash paid			(5)
Reserve balance	$ 1		$ 1		$ 1

Restructuring - Additional Information (Detail)		1 Months Ended	3 Months Ended			9 Months Ended		12 Months Ended	13 Months Ended	81 Months Ended
Restructuring - Additional Information (Detail)	Apr. 26, 2013 Employees	Jun. 30, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2014 USD ($)
Restructuring Cost and Reserve [Line Items]
Pre-tax charge to earnings				$ 2,000,000	$ 4,000,000	$ 14,000,000	$ 24,000,000
Expected cumulative net cash outlays related to plan		$ 22,000,000		22,000,000		22,000,000			$ 22,000,000	$ 22,000,000
Cash payments				5,000,000		20,000,000			19,000,000
Restructuring costs in accrued expenses		10,000,000		10,000,000		10,000,000			10,000,000	10,000,000	$ 13,000,000	$ 19,000,000
Restructuring Activities Other [Member]
Restructuring Cost and Reserve [Line Items]
Pre-tax charge to earnings				1,000,000		6,000,000	6,000,000
Maximum [Member] \| Restructuring Activities Other [Member]
Restructuring Cost and Reserve [Line Items]
Pre-tax charge to earnings					2,000,000
Scenario, Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Expected cumulative net cash outlays related to plan			$ 3,000,000					$ 3,000,000
Additional restructuring charges after current fiscal			1,000,000
Severance and Employee Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Pre-tax charge to earnings				2,000,000		7,000,000
Severance charges				14,000,000		1,000,000	14,000,000		12,000,000
Cash payments				5,000,000		15,000,000
Restructuring costs in accrued expenses		6,000,000		6,000,000		6,000,000			6,000,000	6,000,000	9,000,000	16,000,000
Severance and Employee Benefits [Member] \| Scenario, Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges			2,000,000
Other Transition Costs [Member]
Restructuring Cost and Reserve [Line Items]
Other charges				8,000,000		4,000,000	1,000,000		7,000,000
Other Transition Costs [Member] \| Scenario, Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Other charges			1,000,000
Environmental Remediation [Member]
Restructuring Cost and Reserve [Line Items]
Pre-tax charge to earnings						1,000,000
Restructuring costs in accrued expenses		3,000,000		3,000,000		3,000,000			3,000,000	3,000,000	$ 3,000,000	$ 2,000,000
Severance Costs [Member] \| Restructuring Activities Other [Member]
Restructuring Cost and Reserve [Line Items]
Cash payments						4,000,000
Accrued severance charges		4,000,000		4,000,000		4,000,000			4,000,000	4,000,000
Severance Costs [Member] \| Scenario, Forecast [Member] \| Restructuring Activities Other [Member]
Restructuring Cost and Reserve [Line Items]
Cash payments			5,000,000
Shared Service Center Transition [Member]
Restructuring Cost and Reserve [Line Items]
Pre-tax charge to earnings				1,000,000	1,000,000	5,000,000	15,000,000		23,000,000
Restructuring costs in accrued expenses		3,000,000		3,000,000		3,000,000			3,000,000	3,000,000
Shared Service Center Transition [Member] \| Scenario, Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Pre-tax charge to earnings								24,000,000
Shared Service Center Transition [Member] \| Severance and Employee Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges									16,000,000
Shared Service Center Transition [Member] \| Severance and Employee Benefits [Member] \| Scenario, Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges								16,000,000
Shared Service Center Transition [Member] \| Other Transition Costs [Member]
Restructuring Cost and Reserve [Line Items]
Other charges									7,000,000
Shared Service Center Transition [Member] \| Other Transition Costs [Member] \| Scenario, Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Other charges								$ 8,000,000
Closure of Port Dickson [Member]
Restructuring Cost and Reserve [Line Items]
Severance charges						2,000,000
Other charges						1,000,000
Expected cumulative net cash outlays related to plan		5,000,000		5,000,000		5,000,000			5,000,000	5,000,000
Equity share in CMSB	50.10%
Affected employees \| Employees	90
Pre-tax charge to earnings		$ 18,000,000		$ 18,000,000		18,000,000			$ 18,000,000	$ 18,000,000
Accelerated depreciation and asset write-offs						$ 15,000,000
Portion of the charges that are allocable to the noncontrolling interest		49.90%		49.90%		49.90%			49.90%	49.90%
Site demolition, clearing and environmental remediation costs						$ 2,000,000
Closure of Port Dickson [Member] \| Maximum [Member]
Restructuring Cost and Reserve [Line Items]
Other charges				$ 1,000,000	1,000,000	1,000,000	2,000,000
Restructuring costs in accrued expenses		$ 1,000,000		1,000,000		1,000,000			$ 1,000,000	$ 1,000,000
Closure of Port Dickson [Member] \| Scenario, Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Cash payments			1,000,000
Expected proceeds from the sale of land						8,000,000
Closure of Port Dickson [Member] \| Scenario, Forecast [Member] \| Land [Member]
Restructuring Cost and Reserve [Line Items]
Expected gain from land sale to partially offset restructuring charges						2,000,000
Closure of Port Dickson [Member] \| Severance and Employee Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Expected cumulative net cash outlays related to plan		2,000,000		2,000,000		2,000,000			2,000,000	2,000,000
Closure of Port Dickson [Member] \| Environmental Remediation [Member]
Restructuring Cost and Reserve [Line Items]
Expected cumulative net cash outlays related to plan		2,000,000		2,000,000		2,000,000			2,000,000	2,000,000
Closure of Port Dickson [Member] \| Facility Closure Costs [Member]
Restructuring Cost and Reserve [Line Items]
Expected cumulative net cash outlays related to plan		1,000,000		1,000,000		1,000,000			1,000,000	1,000,000
Closure of Port Dickson [Member] \| Severance Costs [Member]
Restructuring Cost and Reserve [Line Items]
Cash payments		4,000,000
Previous Actions and Sites Pending Sale [Member]
Restructuring Cost and Reserve [Line Items]
Pre-tax charge to earnings						2,000,000	$ 6,000,000
Severance charges		67,000,000
Other charges		23,000,000
Cash payments										86,000,000
Pre-tax charge to earnings		165,000,000		165,000,000		165,000,000			165,000,000	165,000,000
Expected gain from land sale to partially offset restructuring charges		1,000,000
Site demolition, clearing and environmental remediation costs		10,000,000
Restructuring accelerated depreciation and asset impairments		66,000,000
Previous Actions and Sites Pending Sale [Member] \| Maximum [Member]
Restructuring Cost and Reserve [Line Items]
Pre-tax charge to earnings				1,000,000	$ 1,000,000
Previous Actions and Sites Pending Sale [Member] \| Scenario, Forecast [Member]
Restructuring Cost and Reserve [Line Items]
Cash payments			$ 3,000,000
Previous Actions and Sites Pending Sale [Member] \| Severance Costs [Member] \| Restructuring Activities Other [Member]
Restructuring Cost and Reserve [Line Items]
Accrued severance charges		$ 2,000,000		$ 2,000,000		$ 2,000,000			$ 2,000,000	$ 2,000,000

Financial Instruments and Fair Value Measurements - Additional Information (Detail) - USD ($)	9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2014
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	1,010,000,000		$ 1,050,000,000
Fixed Rate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of long-term debt	960,000,000		980,000,000
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	$ 12,000,000		$ 13,000,000

Derivative - Additional Information (Detail) - USD ($)	Jun. 30, 2015	Sep. 30, 2014
Fair Value Hedging [Member] \| Interest Rate Swap-Fixed to Variable [Member]
Derivative [Line Items]
Derivatives held to manage interest rate risk	$ 0	$ 0

Derivatives - Schedule of Derivatives Foreign Currency (Detail) - USD ($)
$ in Millions

Jun. 30, 2015

Sep. 30, 2014

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

Derivative [Line Items]

Notional amount, net of forward foreign currency contract no designation hedge derivatives

^[1]

$ 1

$ 32

[1]	Cabot’s forward foreign exchange contracts are denominated primarily in the Brazilian real, British pound sterling, Czech koruna, Indonesian rupiah, and Mexican peso.

Venezuela - Additional Information (Detail) in Millions	9 Months Ended
Venezuela - Additional Information (Detail) in Millions	Jun. 30, 2015 USD ($) Bs. / $	Jun. 30, 2014 USD ($)	Jun. 30, 2015 VEF ( ) Bs. / $
Nature Of Operations [Line Items]
Operating affiliate investment	$ 15,000,000
Due from affiliates, dividends cash \|			18
Conversion of Bolivars to USD \| Bs. / $	52		52
Subsidiaries [Member]
Nature Of Operations [Line Items]
Cash dividend received from subsidiary	$ 5,000,000	$ 4,000,000
Maximum [Member]
Nature Of Operations [Line Items]
Due from affiliates, dividends cash	$ 1,000,000
Carbon Black Affiliate [Member] \| Venezuela [Member]
Nature Of Operations [Line Items]
Equity method investment, ownership percentage	49.00%		49.00%

Financial Information by Segment - Additional Information (Detail)	1 Months Ended		9 Months Ended
	Dec. 31, 2014 Segments	Dec. 31, 2014 Segment	Jun. 30, 2015 Segment Business_Unit
Segment Reporting Information [Line Items]
Number of aggregated business segment	4	4
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Number of aggregated business segment \| Segment			1
Number of business activity \| Business_Unit			2

Financial Information by Segment - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Revenues from external customers	$ 694	$ 940	$ 2,200	$ 2,736
Income (loss) from continuing operations before taxes	(509)	80	(419)	237
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	669	902	2,124	2,653
Income (loss) from continuing operations before taxes	86	109	252	339
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	25	38	76	83
Income (loss) from continuing operations before taxes	(595)	(29)	(671)	(102)
Reinforcement Materials [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	351	538	1,169	1,583
Income (loss) from continuing operations before taxes	32	62	112	200
Performance Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	234	262	700	763
Income (loss) from continuing operations before taxes	48	44	129	127
Purification Solutions [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	72	78	219	230
Income (loss) from continuing operations before taxes	3	(7)	3	(20)
Specialty Fluids [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	12	24	36	77
Income (loss) from continuing operations before taxes	$ 3	$ 10	$ 8	$ 32

Financial Information by Segment - Financial Information by Reportable Segment (Parenthetical) (Detail)	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting [Abstract]
Percentage of sale of an equity method affiliate	100.00%	100.00%	100.00%	100.00%

Financial Information by Segment - Sales of Equity Method Affiliate and Discounting Charges for Certain Notes Receivable (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Net sales	$ 694	$ 940	$ 2,200	$ 2,736
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Net sales	25	38	76	83
Unallocated and Other [Member] \| Royalties, Other Operating Revenues, 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]
Net sales	(5)	10	(9)	(2)
Unallocated and Other [Member] \| Shipping and Handling Costs [Member]
Segment Reporting Information [Line Items]
Net sales	$ 30	$ 28	$ 85	$ 85

Financial Information by Segment - Sales of Equity Method Affiliate and Discounting Charges for Certain Notes Receivable (Parenthetical) (Detail)	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting [Abstract]
Percentage of sale of an equity method affiliate	100.00%	100.00%	100.00%	100.00%

Financial Information by Segment - Schedule of Income (Loss) from Continuing Operations before Taxes for Unallocated and Other (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Interest expense	$ (13)	$ (14)	$ (40)	$ (41)
Equity in (earnings) loss of affiliated companies, net of tax			4	(2)
(Loss) income from continuing operations	(509)	80	(419)	237
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Interest expense	(13)	(14)	(40)	(41)
Total certain items, pre-tax	(567)	(7)	(599)	(19)
Equity in (earnings) loss of affiliated companies, net of tax	(1)	2	(4)	2
Unallocated corporate costs	(12)	(14)	(35)	(43)
General unallocated income (expense)	(2)	4	7	(1)
(Loss) income from continuing operations	$ (595)	$ (29)	$ (671)	$ (102)

Financial Information by Segment - Schedule of Income (Loss) from Continuing Operations before Taxes for Unallocated and Other (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Restructuring charges	$ 2	$ 4	$ 14	$ 24
Asset Impairment Charges			482
Employee benefit plan settlement charge			18
Non-cash gain on acquisition				29
Certain Item [Member]
Segment Reporting Information [Line Items]
Restructuring charges	2	3	14	24
Asset Impairment Charges	563		563
Acquisition and integration related charges			2	5
Employee benefit plan settlement charge			18
One-time integration costs				3
Acquisition of accounting adjustments for acquired inventory				2
Reserves for environmental matters		1		16
Foreign currency exchange rate, re measurement income (loss)	$ 2	$ 3	$ 2	3
Non-cash gain on acquisition				$ 29

Financial Information by Segment - Schedule of Performance Segment (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Segment Reporting Information [Line Items]
Net sales	$ 694	$ 940	$ 2,200	$ 2,736
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	669	902	2,124	2,653
Performance Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	234	262	700	763
Performance Chemicals [Member] \| Specialty Carbons and Formulations [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	159	182	478	531
Performance Chemicals [Member] \| Metal Oxides [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	$ 75	$ 80	$ 222	$ 232

Commitments and Contingencies - Schedule of Components of Purchase Commitments (Detail) $ in Millions	Jun. 30, 2015 USD ($)
Long-term Purchase Commitment [Line Items]
Payments Due by Remainder of Fiscal Year 2015	$ 112
Payments Due by Fiscal Year 2016	300
Payments Due by Fiscal Year 2017	225
Payments Due by Fiscal Year 2018	217
Payments Due by Fiscal Year 2019	213
Payments Due Thereafter	2,129
Payments Due, Total	3,196
Reinforcement Materials [Member]
Long-term Purchase Commitment [Line Items]
Payments Due by Remainder of Fiscal Year 2015	86
Payments Due by Fiscal Year 2016	227
Payments Due by Fiscal Year 2017	178
Payments Due by Fiscal Year 2018	177
Payments Due by Fiscal Year 2019	173
Payments Due Thereafter	1,911
Payments Due, Total	2,752
Performance Chemicals [Member]
Long-term Purchase Commitment [Line Items]
Payments Due by Remainder of Fiscal Year 2015	19
Payments Due by Fiscal Year 2016	60
Payments Due by Fiscal Year 2017	38
Payments Due by Fiscal Year 2018	33
Payments Due by Fiscal Year 2019	33
Payments Due Thereafter	210
Payments Due, Total	393
Purification Solutions [Member]
Long-term Purchase Commitment [Line Items]
Payments Due by Remainder of Fiscal Year 2015	7
Payments Due by Fiscal Year 2016	13
Payments Due by Fiscal Year 2017	9
Payments Due by Fiscal Year 2018	7
Payments Due by Fiscal Year 2019	7
Payments Due Thereafter	8
Payments Due, Total	$ 51