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Tokai Carbon's Registered Capital [Member] Amendment Flag Amendment Flag Short-Term Debt, Total Short-term borrowings Short Term Borrowings Plus: Earnings allocated to participating securities Participating Securities Distributed And Undistributed Earnings Loss Diluted Accumulated Amortization Finite Lived Intangible Assets Accumulated Amortization Goodwill, Total Goodwill Beginning balance Ending balance Goodwill Deferred income taxes Deferred Income Tax Assets Net Schedule of Intangible Assets Schedule Of Finite Lived Intangible Assets Table [Text Block] (Gains) losses reclassified to interest expense Total before tax Reclassification From Accumulated Other Comprehensive Income Current Period Before Tax Disposal Group Name Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Axis] Document Quarterly Report Document Quarterly Report Purchases of common stock Payments For Repurchase Of Common Stock Release of Currency Translation Adjustment [Member] Currency Translation Adjustment [Member] Accumulated Translation Adjustment [Member] Equity affiliates Equity Method Investments Statement [Table] Statement [Table] Other Comprehensive Income (Loss), Tax, Total Net of tax Other Comprehensive Income Loss Tax Common Stock, Net of Treasury Stock [Member] Common Stock Net Of Treasury Stock [Member] Common stock net of treasury stock. 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Gain on bargain purchase of a business Gain on bargain purchase of a business (Note C) Gain on bargain purchase of a business (Note C) Gain Loss On Sale Of Business Acquisition Business Combination Disclosure [Text Block] Beginning Balance, Shares Ending Balance, Shares Shares Issued Income Tax Authority Income Tax Authority [Domain] 3.7% Notes due fiscal 2022 [Member] Three Point Seven Percentage Notes Due In Two Thousand And Twenty Two [Member] Three point seven percentage notes due in two thousand and twenty two. 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Preferred stock, authorized shares Preferred Stock Shares Authorized Fair value of long-term debt Long Term Debt Fair 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 Certain Items [Member] Corporate Non Segment [Member] Investment, Name [Domain] Entity Small Business Entity Small Business Number of business reportable segments Number Of Reportable Segments Goodwill And Intangible Assets [Line Items] Goodwill And Intangible Assets [Line Items] Goodwill and intangible assets. 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Entity File Number Entity File Number Statement Of Cash Flows [Abstract] Geographical Segment Geographical [Domain] Calculation of Undistributed Earnings Schedule Of Earnings Per Share Basic By Common Class [Text Block] Statistical Measurement Range [Member] Statement Of Stockholders Equity [Abstract] Respirator reserve Respirator Reserve The estimated aggregate amount of losses related to respirator liability claims as of the balance sheet date. Legal Entity Legal Entity [Axis] Purchase and retirement of common stock, Shares Stock Repurchased And Retired During Period Shares Stockholders Equity Note [Abstract] Business acquisition, ownership percentage Equity Method Investment Ownership Percentage Goodwill And Intangible Assets [Table] Goodwill And Intangible Assets [Table] Goodwill and intangible assets. 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[Member] Tokai Carbon Group Tianjin Co [Member] Tokai Carbon Group(Tianjin) Co. 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Asia Pacific [Member] Asia Pacific [Member] Entity Current Reporting Status Entity Current Reporting Status Foreign currency impact Goodwill Foreign Currency Translation Gain Loss Total inventories Inventory Net Americas [Member] Americas [Member] Asset Impairment Charges, Total 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 Business Combinations [Abstract] Finite-Lived Intangible Assets, Net, Ending Balance Finite-Lived Intangible Assets, Net, Beginning Balance Net Intangible Assets, finite lives Intangible assets, net Finite Lived Intangible Assets Net Diluted EPS: Earnings Per Share Diluted [Abstract] Stockholders' Equity Attributable to Parent, Ending Balance Stockholders' Equity Attributable to Parent, Beginning Balance Total Cabot Corporation stockholders' equity Stockholders Equity Accumulated Other Comprehensive Income (Loss) [Member] Accumulated Other Comprehensive Income [Member] Pepinster, Belgium [Member] BELGIUM Effect of Exchange Rate on Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents, Including Disposal Group and Discontinued Operations, Total 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 Entity Tax Identification Number Entity Tax Identification Number Income Statement Location Income Statement Location [Axis] Authorized: 200,000,000 shares of $1 par value, Issued: 56,282,299 and 56,385,963 shares, Outstanding: 56,146,164 and 56,248,559 shares Common Stock Value Consolidation Items Consolidation Items [Axis] Retained Earnings (Accumulated Deficit), Total Retained earnings Retained Earnings Accumulated Deficit Equity Components Statement Equity Components [Axis] Contingencies Loss Contingency Disclosures Accounts Payable and Accrued Liabilities [Member] Accounts Payable And Accrued Liabilities [Member] Customer Relationships [Member] Customer Relationships [Member] Percentage of sale of an equity method affiliate Percentage Of Sale Of Equity Method Affiliates Percentage of sale of equity method affiliates. 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Statement Of Income And Comprehensive Income [Abstract] Property, Plant and Equipment, Net, Total Property, plant and equipment, net Property Plant And Equipment Net Debt Instrument, Unamortized Discount, Total Debt instrument, discount Debt Instrument Unamortized Discount Statement [Line Items] Statement [Line Items] Shares Issued, Value, Share-Based Payment Arrangement, after Forfeiture, Total Issuance of stock under equity compensation plans Stock Issued During Period Value Share Based Compensation Other Other Certain Items Other certain items. 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Developed Technologies [Member] Developed Technology Rights [Member] Income Tax Authority Income Tax Authority [Axis] Net income (loss) Net income (loss) Profit Loss Current assets: Assets Current [Abstract] Dividends, Common Stock, Total Less: Dividends declared on common stock Dividends Common Stock Amortization expense estimated for year four Finite Lived Intangible Assets Amortization Expense Year Four Other comprehensive income (loss) before reclassifications Other Comprehensive Income Loss Before Reclassifications Net Of Tax Amortization expense estimated for year two Finite Lived Intangible Assets Amortization Expense Year Two Financial Information by Segment Segment Reporting Disclosure [Text Block] One Equity Partners [Member] One Equity Partners [Member] One Equity Partners. Schedule Of Goodwill [Text Block] Schedule of Changes in Balances Fair Value Hierarchy and NAV Fair Value Measurements Fair Value Hierarchy [Domain] Changes in assets and liabilities: Increase Decrease In Operating Capital [Abstract] Gain on sale of land Gain on sale of land Gain Loss On Sale Of Land Gain (loss) on sale of land. Entity Entity [Domain] Income (loss) before income taxes Income (loss) before income taxes and equity in earnings of affiliated companies Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments Cover [Abstract] Product and Service Products And Services [Domain] Insurance proceeds recorded Unusual Or In frequent Item Insurance Proceeds Recorded Unusual or in frequent item insurance proceeds recorded. Undistributed earnings (loss) Undistributed Earnings Finished goods Inventory Finished Goods Fair value, liabilities, Level 2 to Level 1 transfers, amount Fair Value Liabilities Level2 To Level1 Transfer Amount Fair value ​liabilities ​level 2 to​ level 1 transfer amount. Inventories: Inventory Net [Abstract] Current liabilities: Liabilities Current [Abstract] Disposal Group Name Disposal Groups Including Discontinued Operations Name [Domain] Maximum [Member] Maximum [Member] Cash provided (used) by investing activities Net Cash Provided By Used In Investing Activities Goodwill and Intangible Assets Goodwill And Intangible Assets Disclosure [Text Block] Accounts Payable and Accrued Liabilities, Current, Total Accounts payable and accrued liabilities Accounts Payable And Accrued Liabilities Current Pension and Other Postretirement Benefit Liability Adjustments [Member] Accumulated Defined Benefit Plans Adjustment [Member] Unsecured notes issued Notes Issued1 Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Noncontrolling Interest, Total Less: Other comprehensive income (loss) attributable to noncontrolling interests Other Comprehensive Income Loss Net Of Tax Portion Attributable To Noncontrolling Interest Fair value, assets, transfers out of Level 3, amount Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Transfers Out Of Level3 Amortization expense estimated for year five Finite-Lived Intangible Asset, Expected Amortization, Year Five Less: Participating securities Participating Securities Unvested restricted stock and stock unit awards that receive non-forfeitable rights to dividends or dividend equivalents. Unallocated and Other [Member] Material Reconciling Items [Member] Non-U.S. Jurisdictions [Member] Foreign Country [Member] Foreign Jurisdictions [Member] Carrying value of long-term debt Debt Instrument Carrying Amount Amortization expense estimated for year three Finite Lived Intangible Assets Amortization Expense Year Three Common stock, authorized shares Common Stock Shares Authorized Other Comprehensive Income (Loss), Net Investment Hedge, Gain (Loss), Reclassification, before Tax Gain associated with the net investment hedge out of AOCI Gain associated with the net investment hedges out of AOCI Derivative assets (liabilities) net, at fair Value Derivative Assets (Liabilities), at Fair Value, Net, Total Derivative Assets Liabilities At Fair Value Net Trading Symbol Trading Symbol Earnings (loss) allocated to common shareholders (numerator) Net Income Loss Available To Common Stockholders Diluted Amounts Reclassified Out of AOCI Reclassification Out Of Accumulated Other Comprehensive Income Table [Text Block] 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] (Gains) Losses Reclassified to Interest Expense [Member] Accumulated Gain Loss Net Cash Flow Hedge Parent [Member] Total Cabot Corporation Stockholders' Equity [Member] Parent [Member] Selling, General and Administrative Expense, Total Selling and administrative expenses Selling General And Administrative Expense Balance Sheet Location Balance Sheet Location [Axis] Comprehensive income (loss) attributable to Cabot Corporation Comprehensive Income Net Of Tax General unallocated income (expense) General Unallocated Income Expense General unallocated income expense. Reinforcement Materials [Member] Reinforcement Materials [Member] Reinforcement materials. Accumulated Other Comprehensive Income Loss [Line Items] Accumulated Other Comprehensive Income Loss [Line Items] United States Internal Revenue Service (IRS) [Member] Internal Revenue Service I R S [Member] Recently Adopted Accounting Standards Recently Adopted Accounting Standards Policy [Text Block] Recently adopted accounting standards. Cash dividends declared to noncontrolling interests Minority Interest Decrease From Distributions To Noncontrolling Interest Holders Common stock, par value Common Stock Par Or Stated Value Per Share 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. Derivative Instrument Derivative Instrument Risk [Axis] Long-Term Debt, Type Longterm Debt Type [Domain] Antidilutive securities excluded from computation of earnings per share Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount