Document Transition Report Document Transition Report Geographical [Axis] Geographical Noncontrolling Interest [Member] Noncontrolling Interests [Member] Tokai Carbon's Registered Capital [Member] Tokai Carbon registered capital. Tokai Carbon Registered Capital [Member] Tokai Carbon's Registered Capital [Member] Other Liabilities, Noncurrent Other liabilities Schedule of Segment Reporting Information, by Segment [Table] Schedule Of Segment Reporting Information By Segment [Table] Increase (Decrease) in Prepaid Expense and Other Assets Prepaid expenses and other assets Weighted Average Number of Shares Issued, Basic Weighted average common shares and participating securities outstanding Finite-Lived Intangible Asset, Expected Amortization, Year Two Amortization expense estimated for year two Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), after Reclassification and Tax [Abstract] Derivatives: net investment hedges Weighted Average [Member] Weighted Average [Member] Revenue from Contract with Customer, Excluding Assessed Tax Net sales Proceeds from Short-Term Debt Proceeds from short-term borrowings Proceeds from Short-Term Debt, Total Cash paid for acquisition of business, net of cash acquired of $- and $5 Payments to Acquire Businesses, Net of Cash Acquired Businesses acquisition, net of cash acquired Payments to Acquire Businesses, Net of Cash Acquired, Total Schedule of Business Acquisitions, by Acquisition [Table] Schedule Of Business Acquisitions By Acquisition [Table] Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Transfers Into Level 3 Fair value, assets, transfers into Level 3, amount Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] Release of Actuarial Losses and Prior Service Cost (Credit) [Member] Common stock net of treasury stock. Common Stock Net Of Treasury Stock [Member] Common Stock, Net of Treasury Stock [Member] Asset impairment charges after tax. Asset Impairment Charges After Tax Impairment charge after tax Common Stock, Dividends, Per Share, Cash Paid Common stock, cash dividends paid, per share Performance chemicals. Performance Chemicals [Member] Performance Chemicals [Member] Net Income (Loss) Attributable to Noncontrolling Interest Net income (loss) attributable to noncontrolling interests, net of tax Net Income (Loss) Attributable to Noncontrolling Interest, Total Less cost of 135,832 and 137,404 shares of common treasury stock Treasury Stock, Common, Value Disposal Groups, Including Discontinued Operations [Table] Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Table] Accumulated Gain (Loss), Net, Cash Flow Hedge, Parent [Member] (Gains) Losses Reclassified to Interest Expense [Member] Debt Instrument, Unamortized Discount Debt instrument, discount Debt Instrument, Unamortized Discount, Total Three point seven percentage notes due in two thousand and twenty two. Three Point Seven Percentage Notes Due In Two Thousand And Twenty Two [Member] 3.7% Notes due fiscal 2022 [Member] Balance Sheet Location [Axis] Balance Sheet Location Assets, Current Total current assets Liabilities and Equity Total liabilities and stockholders' equity Entity Address, State or Province Entity Address, State or Province Deferred Income Tax Assets, Net Deferred income taxes Comprehensive Income (Loss), Net of Tax, Attributable to Parent Comprehensive income (loss) attributable to Cabot Corporation Trading Symbol Trading Symbol Common Stock, Shares, Issued Common stock, issued shares Proceeds from Sale, Land, Held-for-Use Proceeds from sale of land Prepaid Expense and Other Assets, Current Prepaid expenses and other current assets Shipping and Handling [Member] Shipping and Handling Costs [Member] Foreign Jurisdictions [Member] Foreign Tax Authority [Member] Non-U.S. Jurisdictions [Member] AOCI Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Member] Business Combination Disclosure [Text Block] Acquisition Dividends, Preferred Stock Less: Dividends declared on participating securities Dividends, Preferred Stock, Total Other comprehensive income (loss), net of tax of $-, $ -, $- and ($1) Other Comprehensive Income (Loss), Net of Tax Total other comprehensive income (loss) Long-Term Debt, Current Maturities Current portion of long-term debt Long-Term Debt, Current Maturities, Total Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent Foreign currency translation adjustment, net of tax Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent, Total Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income Loss [Line Items] Entity Address, City or Town Entity Address, City or Town Schedule of Earnings Per Share, Basic, by Common Class, Including Two Class Method [Table Text Block] Calculation of Undistributed Earnings Increase (Decrease) in Income Taxes Payable Income taxes payable Disposal Group Name [Axis] Disposal Group Name Reclassification out of Accumulated Other Comprehensive Income [Table] Reclassification Out Of Accumulated Other Comprehensive Income [Table] Payments of Ordinary Dividends, Common Stock Cash dividends paid to common stockholders Additional Paid-in Capital [Member] Additional Paid-in Capital [Member] Schedule of performance segment. Schedule Of Performance Segment Table [Text Block] Schedule of Performance Segment Inventory, Raw Materials, Gross Raw materials Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items] Liabilities, Current [Abstract] Current liabilities: Cash acquired in acquisition of business Cash Acquired from Acquisition Assets, Current [Abstract] Current assets: Preferred Stock, Par or Stated Value Per Share Preferred stock, par value Less: Equity in earnings of affiliated companies, net of tax Income loss from equity method investments net of tax. Income Loss From Equity Method Investments Net Of Tax Less: Equity in earnings of affiliated companies, net of tax Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Total before tax (Gains) losses reclassified to interest expense Statement of Stockholders' Equity [Abstract] Debt Instrument, Maturity Date Debt maturity date Goodwill and intangible assets. Goodwill And Intangible Assets [Line Items] Goodwill And Intangible Assets [Line Items] Derivative Contract [Domain] Derivative Contract Property, Plant and Equipment, Net Property, plant and equipment, net Property, Plant and Equipment, Net, Total Statement of Comprehensive Income [Abstract] Treasury Stock, Common, Shares Common treasury stock, shares Entity Central Index Key Entity Central Index Key Fair​ value ​assets level 2 to ​level 1 transfer amount. Fair Value Assets Level2 To Level1 Transfer Amount Fair value, assets, Level 2 to Level 1 transfers, amount Tokai Carbon. Tokai Carbon [Member] Tokai Carbon [Member] Net discrete tax benefits charges related to tax settlements. Net Discrete Tax Benefits Charges Related To Tax Settlements Net discrete tax (benefits) expense related to tax settlements Preferred Stock, Shares Outstanding Preferred stock, Outstanding shares Preferred Stock, Shares Outstanding, Beginning Balance Preferred Stock, Shares Outstanding, Ending Balance Schedule of Changes in Balances Schedule of Goodwill [Table Text Block] Liabilities, Current Total current liabilities Entity Tax Identification Number Entity Tax Identification Number Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income from continuing operations before income taxes and equity in earnings of affiliated companies Increase (Decrease) in Operating Capital [Abstract] Changes in assets and liabilities: Business combination acquisition and integration related costs. Business Combination Acquisition And Integration Related Costs Acquisition and integration-related charges Accounts and notes receivable, net of reserve for doubtful accounts of $2 and $3 Accounts and Financing Receivable, after Allowance for Credit Loss, Current Accounts and notes receivable Accounts and Financing Receivable, after Allowance for Credit Loss, Current, Total Investment, Name [Axis] Derivative Instrument [Axis] Derivative Instrument Geographical [Domain] Geographical Assets Total assets Business Combination, Bargain Purchase, Gain Recognized, Amount Gain on bargain purchase of a business Gain on bargain purchase of a business Entity Registrant Name Entity Registrant Name Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers out of Level 3 Fair value, liabilities, transfers out of Level 3, amount Retained Earnings (Accumulated Deficit) Retained earnings Retained Earnings (Accumulated Deficit), Total Common Stock, Number of Shares, Par Value and Other Disclosure [Abstract] Common stock: Cash provided by operating activities Proceeds from Insurance Settlement, Operating Activities Retained Earnings [Member] Retained Earnings [Member] Equity, Including Portion Attributable to Noncontrolling Interest Ending Balance Beginning Balance Total stockholders' equity Deferred Income Tax Liabilities, Net Deferred income taxes Minimum [Member] Minimum [Member] Revenues Net sales and other operating revenues Revenues from external customers Revenues, Total Parent [Member] Total Cabot Corporation Stockholders' Equity [Member] Significant Accounting Policies [Text Block] Significant Accounting Policies Natural Disasters and Other Casualty Events [Member] Flood [Member] Accrued Income Taxes, Current Income taxes payable Equity Component [Domain] Equity Component Segments [Axis] Segments Unusual or Infrequent Item, or Both [Axis] Unusual or Infrequent Item, or Both Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Adjustments to reconcile net income (loss) to cash provided (used) by operating activities: Goodwill, Foreign Currency Translation Gain (Loss) Foreign currency impact Gain (Loss) on Disposition of Business Gain on bargain purchase of a business (Note C) Gain on bargain purchase of a business (Note C) Gain on bargain purchase of a business Net Income (Loss) Available to Common Stockholders, Diluted Earnings (loss) allocated to common shareholders (numerator) Entity Current Reporting Status Entity Current Reporting Status Common Stock, Shares Authorized Common stock, authorized shares Research and Development Expense Research and technical expenses Research and Development Expense, Total Unusual or Infrequent Item, or Both [Domain] Unusual or Infrequent Item, or Both Long-Term Debt, Fair Value Fair value of long-term debt Divestitures Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Proceeds from Issuance of Common Stock Proceeds from sales of common stock Amortization of Intangible Assets Amortization of intangible assets Additional pre-tax loss on sale of business Additional Pre Tax Loss on Sale of Business Additional Pre Tax Loss on Sale of Business Stock Repurchased and Retired During Period, Value Purchase and retirement of common stock Authorized: 200,000,000 shares of $1 par value, Issued: 56,072,816 and 56,385,963 shares, Outstanding: 55,936,984 and 56,248,559 shares Common Stock, Value, Issued Debt instrument interest payable description. Debt Instrument Interest Payable Description Debt instrument interest payable description Repayments of Long-Term Debt Repayments of long-term debt Repayments of Long-Term Debt, Total Other Noncash Income (Expense) Other non-cash (income) expense Other Noncash Income (Expense), Total Current Fiscal Year End Date Current Fiscal Year End Date Share-based compensation Share-Based Payment Arrangement, Noncash Expense Non-cash compensation Share-Based Payment Arrangement, Noncash Expense, Total Operating Income (Loss) Income (loss) from operations Charges related to value added tax matters. Charges Related To Value Added Tax Matters Charges related to value added tax matters Business Combination, Consideration Transferred Business acquisition, purchase price Business Combination, Consideration Transferred, Total Tax Period [Axis] Tax Period Deferred Income Tax Expense (Benefit) Deferred tax provision (benefit) Deferred Income Tax Expense (Benefit), Total Income Tax Expense (Benefit) (Provision) benefit for income taxes Income Tax Expense (Benefit), Total The estimated aggregate amount of losses related to respirator liability claims as of the balance sheet date. Respirator Reserve Respirator reserve Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Amounts reclassified from AOCI Goodwill and intangible assets. Goodwill And Intangible Assets [Table] Goodwill And Intangible Assets [Table] Increase (Decrease) in Accounts and Notes Receivable Accounts and notes receivable Other comprehensive income (loss) net investment hedges gain (loss) excluded from effectiveness testing and amortized to interest expense, net of tax. Other Comprehensive Income Loss Net Investment Hedges Gain Loss Excluded From Effectiveness Testing And Amortized To Interest Expense Net Of Tax (Gains) losses excluded from effectiveness testing and amortized to interest expense, net of tax Finite-Lived Intangible Assets, Net Intangible assets, net Net Intangible Assets, finite lives Finite-Lived Intangible Assets, Net, Beginning Balance Finite-Lived Intangible Assets, Net, Ending Balance Employee benefit plan settlement and other charges. Employee Benefit Plan Settlement And Other Charges Employee benefit plan settlement and other charges Schedule of Segment Reporting Information, by Segment [Table Text Block] Financial Information by Reportable Segment Accounts Payable and Accrued Liabilities [Member] Accounts Payable and Accrued Liabilities [Member] Disposal Group Name [Domain] Disposal Group Name Marshall Mine [Member] Marshall mine. Marshall Mine [Member] Marshall Mine Respirator liabilities. Respirator Liabilities [Member] Respirator Liabilities [Member] Repayments of short-term borrowings Repayments of Short-Term Debt Repayments of Short-Term Debt, Total Cost of sales, selling and administrative expense and research and technical expense. Cost Of Sales Selling And Administrative Expense And Research And Technical Expense [Member] Cost of Sales, Selling and Administrative Expenses and Research and Technical Expenses [Member] Other Nonoperating Income (Expense) Other income (expense) Other Nonoperating Income (Expense), Total Business Interruption Loss [Line Items] Business Interruption Loss [Line Items] Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Comprehensive income (loss) attributable to noncontrolling interests Revenue from External Customers by Geographic Areas [Table Text Block] Revenues from External Customers by Geographic Region Long-Term Debt, Type [Domain] Long-Term Debt, Type Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Other comprehensive income (loss), net of tax Commitments and Contingencies Disclosure [Abstract] Other Assets, Noncurrent Other assets Five percentage notes due two thousand and thirty two. Five Percentage Notes Due Two Thousand And Thirty Two [Member] 5% Notes due fiscal 2023 [Member] Asia Pacific [Member] Asia Pacific [Member] Finite-Lived Intangible Asset, Expected Amortization, Year Four Amortization expense estimated for year four Finite-Lived Intangible Asset, Expected Amortization, Year One Amortization expense estimated for year one Inventory, Net [Abstract] Inventories: Restructuring charges benefit. Restructuring Charges Benefit Global restructuring activities Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Developed Technology Rights [Member] Developed Technologies [Member] Entity [Domain] Entity Loss Contingency Nature [Axis] Loss Contingency Nature Cost of Goods and Services Sold Cost of sales Cost of Goods and Services Sold, Total Earnings Per Share [Abstract] Earnings (loss) per common share: Loss Contingencies [Table] Loss Contingencies [Table] Investment, Name [Domain] Dividends, Common Stock Less: Dividends declared on common stock Dividends, Common Stock, Total Accounting Policies [Abstract] Segments [Domain] Segments Finite-Lived Intangible Asset, Expected Amortization, Year Five Amortization expense estimated for year five Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Other comprehensive income (loss) before reclassifications Tokai Carbon Group Tianjin Co Tokai Carbon Group(Tianjin) Co. Tokai Carbon Group Tianjin Co [Member] Tokai Carbon Group(Tianjin) Co. [Member] Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Cash dividends declared to noncontrolling interests Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Stockholders' equity: Earnings Per Share, Basic Basic Earnings (loss) per common share - basic: Earnings Per Share, Basic, Total Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Changes in Each Component of AOCI, Net of Tax Commitments and Contingencies Contingencies (Note G) Business Combinations [Abstract] Income Statement [Abstract] Undistributed earnings are adjusted for the assumed distribution of dividends to dilutive securities and then reallocated to the participating securities. Adjusted Earnings Loss Allocated To Participating Securities Less: Adjusted earnings allocated to participating securities Increase (Decrease) in Accounts Payable and Accrued Liabilities Accounts payable and accrued liabilities Increase (Decrease) in Accounts Payable and Accrued Liabilities, Total Statistical Measurement [Domain] Statistical Measurement Loss Contingencies [Line Items] Loss Contingencies [Line Items] Accumulated net investment hedges gain (loss) excluded from effectiveness testing and amortized to interest expense. Accumulated Net Investment Hedges Gain Loss Excluded From Effectiveness Testing And Amortized To Interest Expense [Member] (Gains) Losses Excluded from Effectiveness Testing and Amortized to Interest Expense [Member] Net Cash Provided by (Used in) Operating Activities Cash provided (used) by operating activities Document Period End Date Document Period End Date Statistical Measurement [Axis] Statistical Measurement Stockholders' Equity Note [Abstract] Earnings Per Share, Diluted Diluted Earnings (loss) per common share - diluted: Earnings Per Share, Diluted, Total Product and Service [Domain] Product and Service EMEA [Member] Europe, Middle East and Africa [Member] Internal Revenue Service (IRS) [Member] United States Internal Revenue Service (IRS) [Member] Debt Instrument, Name [Domain] Debt Instrument, Name Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV Open Tax Year Tax years remain subject to examination Earning per share basic and diluted. Earning Per Share Basic And Diluted [Abstract] Weighted-average common shares outstanding: Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Income (loss) before income taxes and equity in earnings of affiliated companies Income (loss) before income taxes Loss Contingency, Nature [Domain] Loss Contingency, Nature Number of Reportable Segments Number of business reportable segments Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member] Pension and Other Postretirement Benefit Liability Adjustments [Member] Loss Contingency, Loss in Period Flood-related expenses Additional Paid in Capital, Common Stock Additional paid-in capital Segment Reconciling Items [Member] Unallocated and Other [Member] Payments for Repurchase of Common Stock Purchases of common stock Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] Amounts Reclassified Out of AOCI Equity, Attributable to Noncontrolling Interest Noncontrolling interests Stockholders' Equity Attributable to Noncontrolling Interest, Total Stockholders' Equity Attributable to Noncontrolling Interest, Beginning Balance Stockholders' Equity Attributable to Noncontrolling Interest, Ending Balance Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name BELGIUM Pepinster, Belgium [Member] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Interactive Data Current Entity Interactive Data Current Proceeds from (Repayments of) Commercial Paper Proceeds from issuance (repayments) of commercial paper, net Proceeds from (Repayments of) Commercial Paper, Total Percentage of sale of equity method affiliates. Percentage Of Sale Of Equity Method Affiliates Percentage of sale of an equity method affiliate Finite-Lived Intangible Asset, Expected Amortization, Year Three Amortization expense estimated for year three Latest Tax Year [Member] Latest Tax Year [Member] Excise tax on stock repurchases. Excise Tax On Stock Repurchases Excise tax on stock repurchases Equity [Abstract] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Earnings Per Share, Basic [Abstract] Basic EPS: Participating Securities, Distributed and Undistributed Earnings (Loss), Diluted Plus: Earnings allocated to participating securities Other Inventory, Gross Other Other Inventory, Gross, Total Equity Components [Axis] Equity Components Fair value ​liabilities ​level 1 to​ level 2 transfer amount. Fair Value Liabilities Level1 To Level2 Transfer Amount Fair value, liabilities, Level 1 to Level 2 transfers, amount Preferred Stock, Number of Shares, Par Value and Other Disclosure [Abstract] Preferred stock: Increase (Decrease) in Other Operating Liabilities Other liabilities Increase (Decrease) in Other Operating Liabilities, Total Payments to Acquire Businesses, Gross Business acquisition, cash consideration Preferred Stock Dividends, Income Statement Impact Less: Dividends and dividend equivalents to participating securities Indirect tax settlement credits. Indirect Tax Settlement Credits Indirect tax settlement credits Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest Less: Other comprehensive income (loss) attributable to noncontrolling interests Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest, Total Fixed rate debt. Fixed Rate Debt [Member] Fixed Rate Debt [Member] Local Phone Number Local Phone Number Goodwill Ending balance Beginning balance Goodwill Goodwill, Total Business Insurance Recoveries [Table] Schedule Of Business Insurance Recoveries [Table] Statement of Cash Flows [Abstract] Stock Repurchased and Retired During Period, Shares Purchase and retirement of common stock, Shares Earliest Tax Year [Member] Earliest Tax Year [Member] Income Tax Authority [Domain] Income Tax Authority Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated other comprehensive income (loss) Accumulated Other Comprehensive Income (Loss), Net of Tax, Total Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Gross Profit Gross profit Accumulated Foreign Currency Adjustment Attributable to Parent [Member] Currency Translation Adjustment [Member] Release of Currency Translation Adjustment [Member] Common Stock, Par or Stated Value Per Share Common stock, par value Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations Effects of exchange rate changes on cash Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations, Total Debt Instrument, Interest Rate, Stated Percentage Interest rate on borrowing Proceeds from Equity Method Investment, Distribution Cash dividends received from equity affiliates Pre-tax loss on sale of business. Pre Tax Loss On Sale Of Business Pre-tax loss on sale Maximum [Member] Maximum [Member] Earnings Per Share, Diluted [Abstract] Diluted EPS: Consolidation Items [Domain] Consolidation Items Dividends Cash dividends paid, Common stock, per share Dividends, Total Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Basis of Presentation Share-based compensation APIC, Share-Based Payment Arrangement, Increase for Cost Recognition APIC, Share-Based Payment Arrangement, Increase for Cost Recognition, Total Share-based compensation Fair Value, Recurring and Nonrecurring [Table] Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Table] Prepaid expenses and other current assets, Accounts payable and accrued liabilities, and Other assets. Prepaid Expenses And Other Current Assets Accounts Payable And Accrued Liabilities And Other Assets [Member] Prepaid Expenses and Other Current Assets Accounts Payable and Accrued Liabilities and Other Assets [Member] Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Increase (decrease) in cash and cash equivalents Accumulated defined benefit plans adjustment net unamortized gain loss and prior service cost credit. Accumulated Defined Benefit Plans Adjustment Net Unamortized Gain Loss And Prior Service Cost Credit [Member] Amortization of Actuarial Losses and Prior Service Cost (Credit) [Member] Fair Value, Measurement with Unobservable Inputs Reconciliation, Liability, Transfers Into Level 3 Fair value, liabilities, transfers into Level 3, amount Payments for (Proceeds from) Other Investing Activities Other Purification solutions. Purification Solutions [Member] Purification Solutions [Member] Proceeds from sale of Purification Solutions business Proceeds from Divestiture of Businesses, Net of Cash Divested Proceeds from sale of business Proceeds from Divestiture of Businesses, Net of Cash Divested, Total Operating Segments [Member] Operating Segments [Member] Other certain items. Other Certain Items Other Segment Reporting Disclosure [Text Block] Financial Information by Segment City Area Code City Area Code Inventory, Net Total inventories Net Cash Provided by (Used in) Operating Activities [Abstract] Cash Flows from Operating Activities: Consolidation Items [Axis] Consolidation Items Other products and services. Other Products And Services [Member] Other [Member] Performance Additives. Performance Additives [Member] Performance Additives [Member] Legal environmental matters and reserves. Legal Environmental Matters And Reserves Legal and environmental matters and reserves Notes Issued Unsecured notes issued Proceeds from long-term debt, net of issuance costs Proceeds from Issuance of Long-Term Debt Proceeds from Issuance of Long-Term Debt, Total Amount excluded from earnings before interest and tax. Amount Excluded From Earnings Before Interest And Tax Total certain items, pre-tax Business Acquisition [Line Items] Business Acquisition [Line Items] Weighted Average Number of Shares Outstanding, Basic Basic Adjusted weighted average common shares (denominator) Adjusted weighted average common shares outstanding Work in process Inventory, Work in Process, Gross Net Cash Provided by (Used in) Financing Activities [Abstract] Cash Flows from Financing Activities: Statement [Table] Statement [Table] Document Fiscal Period Focus Document Fiscal Period Focus Income (Loss) from Equity Method Investments Equity in earnings of affiliated companies, net of tax Equity in earnings of affiliated companies Financial Instruments Disclosure [Text Block] Financial Instruments and Fair Value Measurements Statement [Line Items] Statement [Line Items] Insurance loss proceeds Unusual or Infrequent Item, or Both, Loss, Gross Income taxes. Income Taxes [Table] Income Taxes [Table] Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Antidilutive securities excluded from computation of earnings per share Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations Uncertain tax positions from expirations of statute of limitations Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value, Total Divestiture related charges. Divestiture Related Charges Divestiture related charges Prepaid expenses and other current assets accounts payable and accrued liabilities and other liabilities. Prepaid Expenses And Other Current Assets Accounts Payable And Accrued Liabilities And Other Liabilities [Member] Prepaid Expenses and Other Current Assets Accounts Payable and Accrued Liabilities and Other Liabilities [Member] Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Inventory, Finished Goods, Gross Finished goods Discontinued Operations and Disposal Groups [Abstract] Cover [Abstract] Selling, General and Administrative Expense Selling and administrative expenses Selling, General and Administrative Expense, Total Document Fiscal Year Focus Document Fiscal Year Focus Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3 Fair value, assets, transfers out of Level 3, amount Comprehensive Income (Loss) Note [Text Block] Accumulated Other Comprehensive Income (Loss) ("AOCI") Segment Reporting [Abstract] Proceeds from Divestiture of Businesses Proceeds from divestiture of cash transferred Security Exchange Name Security Exchange Name New Accounting Pronouncements, Policy [Policy Text Block] Recent Accounting Pronouncements Preferred Stock, Shares Issued Preferred stock, Issued shares Preferred Stock, Shares Authorized Preferred stock, authorized shares Customer Relationships [Member] Customer Relationships [Member] Schedule of Finite-Lived Intangible Assets [Table] Schedule Of Finite Lived Intangible Assets [Table] Payments of Ordinary Dividends, Noncontrolling Interest Cash dividends paid to noncontrolling interests ADA Carbon Solutions, LLC . A D A Carbon Solutions L L C [Member] ADA Carbon Solutions, LLC [Member] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree Other Comprehensive Income (Loss), Tax Net of tax Other Comprehensive Income (Loss), Tax, Total Legal Entity [Axis] Legal Entity Unusual or Infrequent Item, or Both, Gain, Gross Insurance gain proceeds Entity Emerging Growth Company Entity Emerging Growth Company Amendment Flag Amendment Flag Undistributed Earnings, Basic Undistributed earnings (loss) Shares, Issued Ending Balance, Shares Beginning Balance, Shares Equity Method Investment, Ownership Percentage Business acquisition, ownership percentage Accumulated defined benefit plans adjustment net settlement charge. Accumulated Defined Benefit Plans Adjustment Net Settlement Charge [Member] Settlement Charge [Member] Unallocated corporate costs are costs not controlled by the segments and primarily benefit corporate interests. Unallocated Corporate Costs Unallocated corporate costs Earnings (Loss) which remain after dividends declared during the period are assumed to be distributed to the common shareholders. Undistributed Loss Earnings Allocated To Participating Shareholders Undistributed earnings allocated to participating shareholders Tax Period [Domain] Tax Period Securities Act File Number Entity File Number Financing Receivable, Allowance for Credit Loss, Current Accounts and notes receivable, reserve for doubtful accounts Prepaid Expenses and Other Current Assets and Other Assets [Member] Prepaid Expenses and Other Current Assets and Other Assets [Member] Prepaid expenses and other current assets and other assets. Goodwill and Intangible Assets Disclosure [Abstract] Contingencies Disclosure [Text Block] Contingencies Gain associated with the net investment hedges out of AOCI Gain associated with the net investment hedge out of AOCI Other Comprehensive Income (Loss), Net Investment Hedge, Gain (Loss), Reclassification, before Tax Long-Term Debt, Excluding Current Maturities Long-term debt Long-Term Debt, Excluding Current Maturities, Total Cash, cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Ending Balance Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Beginning Balance Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Total Debt Instrument [Axis] Debt Instrument Americas [Member] Americas [Member] Income taxes. Income Taxes [Line Items] Income Taxes [Line Items] Preferred Stock, Value, Issued Authorized: 2,000,000 shares of $1 par value, Issued and Outstanding: None and none Entity Small Business Entity Small Business Entity Shell Company Entity Shell Company Earnings Per Share [Text Block] Earnings Per Share Entity Address, Address Line One Entity Address, Address Line One Undistributed Earnings (Loss) Allocated to Participating Securities, Basic Less: Undistributed earnings allocated to participating securities Undistributed Earnings (Loss) Allocated to Participating Securities, Basic, Total Finite-Lived Intangible Assets, Gross Gross Carrying Value, finite lives Finite-Lived Intangible Assets, Gross, Total Restricted cash classified within Prepaid expenses and other current assets Restricted Cash Restricted Cash, Total Income Statement Location [Axis] Income Statement Location Tax expense related to withholding tax accruals on historic earnings. Tax Expense Related To Withholding Tax Accruals On Historic Earnings Tax expense related to withholding tax accruals on historic earnings due to changes in indefinite reinvestment assertion on certain entities Long-Term Debt, Type [Axis] Long-Term Debt, Type Insurance recovery. Insurance Recovery [Abstract] Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net income (loss) Net income (loss) Corporate, Non-Segment [Member] Certain Items [Member] Fair Value, Inputs, Level 2 [Member] Significant Observable Inputs (Level 2) [Member] Product [Member] By-product Sales [Member] Equity Method Investments Equity affiliates Long-Term Debt, Gross Carrying value of long-term debt Depreciation, Depletion and Amortization Depreciation and amortization Depreciation, Depletion and Amortization, Total Product and Service [Axis] Product and Service Title of 12(b) Security Title of 12(b) Security Finite-Lived Intangible Assets, Accumulated Amortization Accumulated Amortization Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture Issuance of stock under equity compensation plans Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture, Total Insurance Settlements Receivable Insurance settlements receivable Schedule of Finite-Lived Intangible Assets [Table Text Block] Schedule of Intangible Assets Insurance proceeds Unusual or Infrequent Item, or Both, Insurance Proceeds Fair​ value ​assets level 1 to ​level 2 transfer​ amount. Fair Value Assets Level1 To Level2 Transfer Amount Fair value, assets, Level 1 to Level 2 transfers, amount Income Tax Authority, Name [Axis] Income Tax Authority, Name Foreign Exchange Contract [Member] Foreign Currency Risks [Member] Trademarks [Member] Trademarks [Member] Net Cash Provided by (Used in) Investing Activities [Abstract] Cash Flows from Investing Activities: Accounts Payable and Accrued Liabilities, Current Accounts payable and accrued liabilities Accounts Payable and Accrued Liabilities, Current, Total State and Local Jurisdiction [Member] State Tax Authorities [Member] Gain (Loss) on Sale of Assets and Asset Impairment Charges Loss on sale of business and asset impairment charge Accounts Payable and Accrued Liabilities Accounts payable and accrued liabilities Accounts Payable and Accrued Liabilities, Total Weighted Average Number of Shares Outstanding, Diluted, Adjustment Common shares issuable Weighted Average Number of Shares Outstanding, Diluted, Adjustment, Total Earnings (loss) which remain after dividends declared during the period are assumed to be distributed to participating shareholders. Undistributed Loss Earnings Allocated To Common Shareholders Undistributed earnings (loss) allocated to common shareholders Increase (Decrease) in Inventories Inventories Increase (Decrease) in Inventories, Total Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Noncontrolling Interest Foreign currency translation adjustment attributable to noncontrolling interests, net of tax Formulated Solutions. Formulated Solutions [Member] Formulated Solutions [Member] Common Stock, Shares, Outstanding Common stock, outstanding shares Common Stock, Shares, Outstanding, Beginning Balance Common Stock, Shares, Outstanding, Ending Balance Short-Term Debt Short-term borrowings Short-Term Debt, Total One Equity Partners. One Equity Partners [Member] One Equity Partners [Member] Income Statement Location [Domain] Income Statement Location Document Type Document Type Gain (loss) on sale of land. Gain Loss On Sale Of Land Gain on sale of land Gain on sale of land Net Cash Provided by (Used in) Investing Activities Cash provided (used) by investing activities Document Quarterly Report Document Quarterly Report Goodwill and Intangible Assets Disclosure [Text Block] Goodwill and Intangible Assets Net Income (Loss) Available to Common Stockholders, Basic Earnings (loss) allocated to common shareholders Earnings (loss) allocated to common shareholders (numerator) Net Cash Provided by (Used in) Financing Activities Cash provided (used) by financing activities Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, after Tax Pension and other postretirement benefit liability adjustments, net of tax Business Insurance Recoveries [Text Block] Insurance Recoveries Unusual or in frequent item insurance proceeds recorded. Unusual Or In frequent Item Insurance Proceeds Recorded Insurance proceeds recorded Entity Filer Category Entity Filer Category Fair value ​liabilities ​level 2 to​ level 1 transfer amount. Fair Value Liabilities Level2 To Level1 Transfer Amount Fair value, liabilities, Level 2 to Level 1 transfers, amount Balance Sheet Location [Domain] Balance Sheet Location Income Tax Authority, Name [Domain] Income Tax Authority, Name Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax (Gains) losses reclassified to interest expense, net of tax Investment Income, Interest and Dividend Interest and dividend income Investment Income, Interest and Dividend, Total Finite-Lived Intangible Asset, Useful Life Useful life of intangible assets Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income Loss [Table] Asset Impairment Charges Loss on sale of business and asset impairment charge (Note D) Impairment charge Loss on sale of business and asset impairment charge (Note D) Asset Impairment Charges, Total Equity, Attributable to Parent Total Cabot Corporation stockholders' equity Stockholders' Equity Attributable to Parent, Beginning Balance Stockholders' Equity Attributable to Parent, Ending Balance Restricted Cash and Cash Equivalents, Current, Statement of Financial Position [Extensible Enumeration] Net income (loss) attributable to Cabot Corporation Net income (loss) attributable to Cabot Corporation Interest Expense Interest expense Interest Expense, Total Unvested restricted stock and stock unit awards that receive non-forfeitable rights to dividends or dividend equivalents. Participating Securities Less: Participating securities Statement of Financial Position [Abstract] Proceeds from insurance settlements Proceeds from Life Insurance Policy Shares Issued, Shares, Share-Based Payment Arrangement, after Forfeiture Issuance of stock under equity compensation plans, Shares Shares Issued, Shares, Share-Based Payment Arrangement, after Forfeiture, Total Weighted Average Number of Shares Outstanding, Diluted Diluted Adjusted weighted average common shares (denominator) Proceeds from Insurance Settlement, Investing Activities Cash provided by investing activities Schedule of Effective Income Tax Rate Reconciliation [Table Text Block] Effective Tax Rate Effective Income Tax Rate Reconciliation, Percent Effective tax rate Effective Income Tax Rate Reconciliation, Percent, Total Derivative Assets (Liabilities), at Fair Value, Net Derivative Assets (Liabilities), at Fair Value, Net, Total Derivative assets (liabilities) net, at fair Value Income Tax Disclosure [Text Block] Income Tax Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items] Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits Employee benefit plan settlement Increase (Decrease) in Obligation, Pension and Other Postretirement Benefits, Total General unallocated income expense. General Unallocated Income Expense General unallocated income (expense) Reinforcement materials. Reinforcement Materials [Member] Reinforcement Materials [Member] Finite-Lived Intangible Assets [Line Items] Finite Lived Intangible Assets [Line Items] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Components of Basic and Diluted Earnings (Loss) Per Common Share (EPS) Recently adopted accounting standards. Recently Adopted Accounting Standards Policy [Text Block] Recently Adopted Accounting Standards Income Tax Authority [Axis] Income Tax Authority Fair Value Disclosures [Abstract] Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Comprehensive income (loss) Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV Payments to Acquire Property, Plant, and Equipment Additions to property, plant and equipment Payments to Acquire Property, Plant, and Equipment, Total Proceeds from Unsecured Notes Payable Proceeds from issuance of unsecured notes Income tax benefit from tax loss related to divestiture. Income Tax Benefit From Tax Loss Related To Divestiture Income tax benefit from tax loss related to divestiture Guarantees, Fair Value Disclosure Other assets in the Consolidated Balance Sheets Business Acquisition [Axis] Business Acquisition Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations, Total Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Income Tax Disclosure [Abstract] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class