Cabot (CBT) 10-Q 5 Feb 21 2021 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Dec. 31, 2020	Feb. 02, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Trading Symbol	CBT
Entity Registrant Name	Cabot Corporation
Entity Central Index Key	0000016040
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		56,616,500
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity File Number	1-5667
Entity Tax Identification Number	04-2271897
Entity Address, Address Line One	Two Seaport Lane
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02210-2019
City Area Code	617
Local Phone Number	345-0100
Security Exchange Name	NYSE
Title of 12(b) Security	Common Stock, $1 par value per share
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes

Consolidated Statements of Oper

Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Net sales and other operating revenues	$ 746	$ 727
Cost of sales	553	586
Gross profit	193	141
Selling and administrative expenses	61	64
Research and technical expenses	14	14
Income (loss) from operations	118	63
Interest and dividend income	2	3
Interest expense	(12)	(14)
Other income (expense)	(9)	(2)
Income (loss) before income taxes and equity in earnings of affiliated companies	99	50
(Provision) benefit for income taxes	(29)	(4)
Net income (loss)	70	46
Net income (loss) attributable to noncontrolling interests, net of tax	10	5
Net income (loss) attributable to Cabot Corporation	$ 60	$ 41
Weighted-average common shares outstanding:
Basic	56.5	56.9
Diluted	56.6	57
Earnings (loss) per common share:
Basic	$ 1.06	$ 0.71
Diluted	$ 1.06	$ 0.70

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 70	$ 46
Other comprehensive income (loss), net of tax
Foreign currency translation adjustment, net of tax	94	43
Derivatives: net investment hedges
(Gains) losses reclassified to interest expense, net of tax	(1)	(1)
Pension and other postretirement benefit liability adjustments, net of tax	3	1
Other comprehensive income (loss)	96	43
Comprehensive income (loss)	166	89
Net income (loss) attributable to noncontrolling interests, net of tax	10	5
Foreign currency translation adjustment attributable to noncontrolling interests, net of tax	7	3
Comprehensive income (loss) attributable to noncontrolling interests, net of tax	17	8
Comprehensive income (loss) attributable to Cabot Corporation	$ 149	$ 81

Consolidated Balance Sheets (Un

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020
Current assets:
Cash and cash equivalents	$ 147	$ 151
Accounts and notes receivable, net of reserve for doubtful accounts of $3 and $2	513	418
Inventories:
Raw materials	107	82
Finished goods	247	225
Other	49	52
Total inventories	403	359
Prepaid expenses and other current assets	62	50
Total current assets	1,125	978
Property, plant and equipment, net	1,353	1,314
Goodwill	142	134
Equity affiliates	41	39
Intangible assets, net	107	103
Deferred income taxes	51	53
Other assets	161	160
Total assets	2,980	2,781
Current liabilities:
Short-term borrowings	13	14
Accounts payable and accrued liabilities	521	488
Income taxes payable	28	20
Current portion of long-term debt	8	7
Total current liabilities	570	529
Long-term debt	1,085	1,094
Deferred income taxes	58	58
Other liabilities	305	286
Commitments and contingencies (Note G)
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: 56,752,165 and 56,616,030 shares, Outstanding: 56,606,215 and 56,466,638 shares	57	57
Less cost of 145,950 and 149,392 shares of common treasury stock	(4)	(4)
Retained earnings	1,032	989
Accumulated other comprehensive income (loss)	(262)	(351)
Total Cabot Corporation stockholders' equity	823	691
Noncontrolling interests	139	123
Total stockholders' equity	962	814
Total liabilities and stockholders' equity	$ 2,980	$ 2,781

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) (Unaudited) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020
Statement Of Financial Position [Abstract]
Accounts and notes receivable, reserve for doubtful accounts	$ 3	$ 2
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	56,752,165	56,616,030
Common stock, outstanding shares	56,606,215	56,466,638
Common treasury stock, shares	145,950	149,392

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash Flows from Operating Activities:
Net income (loss)	$ 70	$ 46
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Depreciation and amortization	39	39
Deferred tax provision (benefit)	(2)	(6)
Employee benefit plan settlement	6
Non-cash compensation	4	1
Other non-cash (income) expense	5
Cash dividends received from equity affiliates		1
Changes in assets and liabilities:
Accounts and notes receivable	(76)	54
Inventories	(37)	(7)
Prepaid expenses and other assets	(10)	(21)
Accounts payable and accrued liabilities	14	3
Income taxes payable	7	(3)
Other liabilities	1	(2)
Cash provided (used) by operating activities	21	105
Cash Flows from Investing Activities:
Additions to property, plant and equipment	(29)	(68)
Cash paid for acquisition of businesses		(8)
Other		(1)
Cash provided (used) by investing activities	(29)	(77)
Cash Flows from Financing Activities:
Proceeds from issuance (repayments) of commercial paper, net		(29)
Proceeds from long-term debt	50	97
Repayments of long-term debt	(66)	(48)
Purchases of common stock	(2)	(34)
Proceeds from sales of common stock	1	1
Cash dividends paid to noncontrolling interests	(1)	(11)
Cash dividends paid to common stockholders	(20)	(20)
Cash provided (used) by financing activities	(38)	(44)
Effects of exchange rate changes on cash	42	20
Increase (decrease) in cash and cash equivalents	(4)	4
Cash and cash equivalents at beginning of period	151	169
Cash and cash equivalents at end of period	$ 147	$ 173

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Millions	Total	Common Stock, Net of Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total Cabot Corporation Stockholders' Equity [Member]	Noncontrolling Interests [Member]
Beginning Balance at Sep. 30, 2019	$ 1,134	$ 52		$ 1,337	$ (391)	$ 998	$ 136
Beginning Balance, Shares at Sep. 30, 2019		57,081
Adoption of accounting standards				3	(3)
Net income (loss)	46			41		41	5
Total other comprehensive income (loss)	43				40	40	3
Cash dividends paid, Common stock, per share	(20)			(20)		(20)
Cash dividends declared to noncontrolling interests	(19)						(19)
Issuance of stock under equity compensation plans	1		$ 1			1
Issuance of stock under equity compensation plans, Shares		273
Amortization of share-based compensation	1		1			1
Purchase and retirement of common stock	(34)		(2)	(32)		(34)
Purchase and retirement of common stock, Shares		(699)
Ending Balance at Dec. 31, 2019	1,152	$ 52		1,329	(354)	1,027	125
Ending Balance, Shares at Dec. 31, 2019		56,655
Beginning Balance at Sep. 30, 2020	814	$ 53		989	(351)	691	123
Beginning Balance, Shares at Sep. 30, 2020		56,467
Net income (loss)	70			60		60	10
Total other comprehensive income (loss)	96				89	89	7
Cash dividends paid, Common stock, per share	(20)			(20)		(20)
Cash dividends declared to noncontrolling interests	(1)						(1)
Issuance of stock under equity compensation plans	1		1			1
Issuance of stock under equity compensation plans, Shares		192
Amortization of share-based compensation	4		4			4
Purchase and retirement of common stock	(2)		(2)			(2)
Purchase and retirement of common stock, Shares		(53)
Amount reclassified to retained earnings in excess of additional paid in capital			$ (3)	3
Ending Balance at Dec. 31, 2020	$ 962	$ 53		$ 1,032	$ (262)	$ 823	$ 139
Ending Balance, Shares at Dec. 31, 2020		56,606

Consolidated Statements of Ch_2

Consolidated Statements of Changes in Stockholders' Equity (Unaudited) (Parenthetical) - $ / shares	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Statement Of Stockholders Equity [Abstract]
Common stock, cash dividends paid, per share	$ 0.35	$ 0.35

Basis of Presentation

Basis of Presentation	3 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	A. Basis of Presentation The consolidated financial statements have been prepared in conformity with accounting policies generally accepted in the United States (“U.S.”) and 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 its fiscal year ended September 30, 2020 (“2020 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 December 31, 2020 and 2019. 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.

Significant Accounting Policies

Significant Accounting Policies	3 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Significant Accounting Policies	B. Significant Accounting Policies Cabot’s significant accounting policies have not materially changed from those described in the 2020 Form 10-K filed with the U.S. Securities and Exchange Commission (“SEC”) on November 25, 2020. Recently Adopted Accounting Standards In June 2016, the FASB issued a new standard on measurement of credit losses. The standard introduces a new "expected loss" impairment model that applies to most financial assets measured at amortized cost and certain other instruments, including trade and other receivables and other financial assets. Entities are required to estimate expected credit losses over the life of financial assets and record an allowance against the assets’ amortized cost basis to present them at the amount expected to be collected. The Company adopted this standard on October 1, 2020. The adoption of this standard did not materially impact the Company’s consolidated financial statements. Recent Accounting Pronouncements In March 2020, the FASB issued a new standard on Reference Rate Reform, which provides temporary optional expedients and exceptions to the existing guidance on contract modifications and hedge accounting to ease the financial reporting burdens related to the expected market transition from the London Interbank Offered Rate ("LIBOR") and other interbank offered rates to alternative reference rates. The standard was effective upon issuance and may generally be applied through December 31, 2022 to any new or amended contracts, hedging relationships, and other transactions that reference LIBOR. The Company is currently evaluating the timing of adoption and the impact of the adoption of this standard on its consolidated financial statements. In December 2019, the FASB issued a new standard Simplifying the Accounting for Income Taxes. The new guidance simplifies the accounting for income taxes by removing several exceptions in the current standard and adding guidance to reduce complexity in certain areas. The new standard is effective for fiscal years beginning after December 15, 2020 and early adoption is permitted. The Company is currently evaluating the timing of adoption and the impact of the adoption of this standard on its consolidated financial statements.

Acquisitions

Acquisitions	3 Months Ended
	Dec. 31, 2020
Business Combinations [Abstract]
Acquisitions	C. Acquisitions Shenzhen Sanshun Nano New Materials Co., Ltd On April 1, 2020, the Company purchased Shenzhen Sanshun Nano New Materials Co., Ltd (SUSN), a leading carbon nanotube producer, for an estimated purchase price of $100 million, consisting of: (i) cash consideration of $84 million, net of $1 million acquired (ii) contingent consideration of $3 million to be paid over the two-year period ending March 31, 2022 upon the satisfaction of certain milestones, and (iii) the assumed debt of $13 million. The debt the Company assumed in the transaction was repaid in June 2020. The operating results of SUSN were included in the results of the Company's Performance Chemicals segment beginning in the third quarter of fiscal 2020.

Employee Benefit Plans

Employee Benefit Plans	3 Months Ended
	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Employee Benefit Plans	D. Employee Benefit Plans Net periodic defined benefit pension costs include the following: Three Months Ended December 31 2020 2019 Pension Benefits U.S. Foreign U.S. Foreign (In millions) Service cost $ — $ 1 $ — $ 1 Interest cost — 1 1 1 Expected return on plan assets — (2 ) (1 ) (2 ) Amortization of actuarial loss — 1 — 1 Settlement charge 6 — — — Net periodic benefit (credit) cost $ 6 $ 1 $ — $ 1 Other postretirement benefit costs were less than $1 million for each of the three months ended December 31, 2020 and 2019. U.S. Cash Balance Plan Termination In fiscal 2019, the Company’s Board of Directors approved a resolution to terminate the Company’s U.S. pension plan. In fiscal 2020 and 2021, the pension liability was settled through a combination of lump-sum payments and purchased annuities, neither of which required an additional cash contribution to the plan. In the fourth quarter of fiscal 2020, the Company recognized a settlement charge of $3 million related to lump-sum payments made to participants who elected this option, which was recorded in Other income (expense) in the Consolidated Statements of Operations. In the first quarter of fiscal 2021, the Company recognized an additional $6 million settlement charge in Other income (expense) related to the final asset transfers through purchased annuities.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	3 Months Ended
	Dec. 31, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	E. Goodwill and Intangible Assets The carrying amount of goodwill attributable to each reportable segment with goodwill balances and the changes in those balances during the three months ended December 31, 2020 are as follows: Reinforcement Materials Performance Chemicals Total (In millions) Balance at September 30, 2020 $ 46 $ 88 $ 134 Foreign currency impact 4 4 8 Balance at December 31, 2020 $ 50 $ 92 $ 142 The following table provides information regarding the Company’s intangible assets: December 31, 2020 September 30, 2020 Gross Carrying Value Accumulated Amortization Net Intangible Assets Gross Carrying Value Accumulated Amortization Net Intangible Assets (In millions) Intangible assets with finite lives Developed technologies $ 63 $ (9 ) $ 54 $ 60 $ (8 ) $ 52 Trademarks 11 (1 ) 10 11 (1 ) 10 Customer relationships 61 (18 ) 43 56 (15 ) 41 Total intangible assets (1) $ 135 $ (28 ) $ 107 $ 127 $ (24 ) $ 103 (1) The increase in value of Total intangible assets as of December 31, 2020 compared to September 30, 2020 was driven by the impact of foreign currency translation. Intangible assets are amortized over their estimated useful lives, which range between ten and twenty-five years, with a weighted average amortization period of approximately eighteen years. Amortization expense for the three months ended December 31, 2020 and 2019 was $2 million and $1 million, respectively, and is included in Cost of sales, Selling and administrative expenses, and Research and technical expense in the Consolidated Statements of Operations. Total amortization expense is estimated to be approximately $8 million each year for the next five fiscal years.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	3 Months Ended
	Dec. 31, 2020
Stockholders Equity Note [Abstract]
Accumulated Other Comprehensive Income (Loss)	F. Accumulated Other Comprehensive Income (Loss) Comprehensive income combines net income (loss) 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, were as follows: Currency Translation Adjustment Pension and Other Postretirement Benefit Liability Adjustments Total (In millions) Balance at September 30, 2020, attributable to Cabot Corporation $ (307 ) $ (44 ) $ (351 ) Other comprehensive income (loss) before reclassifications 94 (1 ) 93 Amounts reclassified from AOCI (1 ) 4 3 Less: Other comprehensive income (loss) attributable to noncontrolling interests 7 — 7 Balance at December 31, 2020, attributable to Cabot Corporation $ (221 ) $ (41 ) $ (262 ) The amounts reclassified out of AOCI and into the Consolidated Statements of Operations in each of the three months ended December 31, 2020 and 2019 were as follows: Affected Line Item in the Consolidated Three Months Ended December 31 Statements of Operations 2020 2019 (In millions) Derivatives: net investment hedges (Gains) losses reclassified to interest expense Interest expense (Note L) $ (1 ) $ (1 ) Pension and other postretirement Amortization of actuarial losses and prior service cost (credit) Net Periodic Benefit Cost (Note D) 1 1 Settlement charge Net Periodic Benefit Cost (Note D) 6 — Total before tax 6 — Tax impact Provision (benefit) for income taxes (3 ) — Total after tax $ 3 $ —

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	G. Commitments and Contingencies Contingencies Respirator Liabilities Cabot has exposure in connection with a safety respiratory products business that a subsidiary acquired from American Optical Corporation (“AO”) in an April 1990 asset purchase transaction. The subsidiary manufactured respirators under the AO brand and disposed of that business in July 1995. In connection with its acquisition of the business, the subsidiary agreed, in certain circumstances, to assume a portion of AO’s liabilities, including costs of legal fees together with amounts paid in settlements and judgments, allocable to AO respiratory products used prior to the 1990 purchase by the Cabot subsidiary. In exchange for the subsidiary’s assumption of certain of AO’s respirator liabilities, AO agreed to provide to the subsidiary the benefits of: (i) AO’s insurance coverage for the period prior to the 1990 acquisition and (ii) a former owner’s indemnity of AO holding it harmless from any liability allocable to AO respiratory products used prior to May 1982. As more fully described in the 2020 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. At no time did this respiratory product line represent a significant portion of the respirator market. In addition to Cabot’s subsidiary, other parties are responsible for significant portions of the costs of these respirator liabilities (as defined in the 2020 10-K, the “Payor Group”). On February 28, 2020, Cabot, with certain members of the Payor Group, entered into a settlement agreement resolving a large group of claims, including claims alleging serious injury, brought by coal workers in Kentucky and West Virginia represented by common legal counsel. The Company’s share of this liability was $65.2 million, and during the second quarter of fiscal 2020, Cabot recorded a charge of $50 million for this settlement, which was included in Selling and administrative expenses in the Consolidated Statements of Operations. The Company paid $32.6 million of the settlement during the third quarter of fiscal 2020 and the remaining $32.6 million in the first quarter of fiscal 2021. Cabot has a reserve to cover its expected share of liabilities for pending and future respirator liability claims, which is included in Other liabilities and Accounts payable and accrued liabilities on the Consolidated Balance Sheets. The Company expects these liabilities to be incurred over a number of years. The reserve was $23 million and $24 million as of December 31, 2020 and September 30, 2020, respectively. The Company’s current estimate of the cost of its share of pending and future respirator liability claims is based on facts and circumstances existing at this time, including the number and nature of the remaining claims. Developments that could affect the Company’s estimate include, but are not limited to, (i) changes in the number of pending and future claims, (ii) changes in the rate of dismissals without payment of pending claims, (iii) significant changes in the average cost of resolving claims, including potential settlements of groups of claims, (iv) significant changes in the legal costs of defending these claims, (v) changes in the nature of claims received or changes in our assessment of the viability of these claims, (vi) trial and appellate outcomes, (vii) changes in the law and procedure applicable to these claims, (viii) the financial viability of the parties that contribute to the payment of respirator claims, (ix) exhaustion or changes in the recoverability of the insurance coverage maintained by certain members of the Payor Group, or a change in the availability of the indemnity provided by a former owner of AO, (x) changes in the allocation of costs among the various parties paying legal and settlement costs, and (xi) a determination that the assumptions that were used to estimate Cabot’s share of liability are no longer reasonable. The Company cannot determine the impact of these potential developments on its current estimate of its share of liability for existing and future claims. Because reserves are limited to amounts that are probable and estimable as of a relevant measurement date, and there is inherent difficulty in projecting the impact of potential developments on Cabot’s share of liability for these existing and future claims, the actual amount of these liabilities for pending and future claims could be different than the reserved amount. Other Matters The Company has various other lawsuits, claims and contingent liabilities arising in the ordinary course of its business and with respect to its divested businesses. The Company does not believe that any of these matters will have a material adverse effect on its financial position; however, litigation is inherently unpredictable. Cabot could incur judgments, enter into settlements or revise its expectations regarding the outcome of certain matters, and such developments could have a material impact on its results of operations in the period in which the amounts are accrued or its cash flows in the period in which the amounts are paid.

Income Tax

Income Tax	3 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Tax	H. Income Tax Effective Tax Rate Three Months Ended December 31 2020 2019 (Dollars in millions) (Provision) benefit for income taxes $ (29 ) $ (4 ) Effective tax rate 29 % 7 % For the three months ended December 31, 2020, the (Provision) benefit for income taxes included a net discrete tax expense of $2 million. For the three months ended December 31, 2019, the (Provision) benefit for income taxes included a net discrete tax benefit of $10 million, which was primarily related to changes in uncertain tax positions as described below and the impact of tax reform legislation in a foreign jurisdiction. 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. 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. Losses from jurisdictions for which no benefit can be recognized are excluded from the overall computations of the estimated annual effective tax rate and a separate estimated annual effective tax rate is computed and applied to ordinary income or loss in the loss jurisdiction. 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. Uncertainties Ca bot and certain subsidiaries are under audit in a number of jurisdictions. In addition, certain statutes of limitations are scheduled to expire in the near future. It is reasonably possible that a further change in the unrecognized tax benefits may also occur within the next twelve months related to the settlement of one or more of these audits or the lapse of applicable statutes of limitations. However, an estimated range of the impact on the unrecognized tax benefits cannot be quantified at this time. Cabot files U.S. federal and state and non-U.S. income tax returns in jurisdictions with varying statutes of limitations. The 2017 through 2019 tax years generally remain subject to examination by the IRS and various tax years from 2005 through 2019 remain subject to examination by the respective state tax authorities. In significant non-U.S. jurisdictions, various tax years from 2003 through 2020 remain subject to examination by their respective tax authorities. During the three months ended December 31, 2020, Cabot released uncertain tax positions of $1 million, due to the expiration of statutes of limitations in various jurisdictions. During the three months ended December 31, 2019, Cabot released uncertain tax positions of $6 million due to the expiration of statutes of limitations in various jurisdictions and accrued for an uncertain tax position of $2 million for a potential settlement.

Earnings Per Share

Earnings Per Share	3 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Earnings Per Share	I. Earnings Per Share The following tables summarize the components of the basic and diluted earnings (loss) per common share (“EPS”) computations: Three Months Ended December 31 2020 2019 (In millions, except per share amounts) Basic EPS: Net income (loss) attributable to Cabot Corporation $ 60 $ 41 Less: Dividends and dividend equivalents to participating securities — — Earnings (loss) allocated to common shareholders (numerator) $ 60 $ 41 Weighted average common shares and participating securities outstanding 57.2 57.7 Less: Participating securities (1) 0.7 0.8 Adjusted weighted average common shares (denominator) 56.5 56.9 Earnings (loss) per common share - basic: $ 1.06 $ 0.71 Diluted EPS: Earnings (loss) allocated to common shareholders $ 60 $ 41 Plus: Earnings allocated to participating securities — — Less: Adjusted earnings allocated to participating securities (2) — — Earnings (loss) allocated to common shareholders (numerator) $ 60 $ 41 Adjusted weighted average common shares outstanding 56.5 56.9 Effect of dilutive securities: Common shares issuable (3) 0.1 0.1 Adjusted weighted average common shares (denominator) 56.6 57.0 Earnings (loss) per common share - diluted: $ 1.06 $ 0.70 (1) Participating securities consist of shares underlying all outstanding and achieved performance-based restricted stock units and all unvested time-based restricted stock units. The holders of these units are entitled to receive dividend equivalents payable in cash to the extent dividends are paid on the Company’s outstanding common stock and equal in value to the dividends that would have been paid in respect of the shares underlying such units. Undistributed earnings are the earnings which remain after dividends declared during the period are assumed to be distributed to the common and participating shareholders. Undistributed earnings are allocated to common and participating shareholders on the same basis as dividend distributions. The calculation of undistributed earnings is as follows: Three Months Ended December 31 2020 2019 (In millions) Calculation of undistributed earnings (loss): Net income (loss) attributable to Cabot Corporation $ 60 $ 41 Less: Dividends declared on common stock 20 20 Less: Dividends declared on participating securities — — Undistributed earnings (loss) $ 40 $ 21 Allocation of undistributed earnings (loss): Undistributed earnings (loss) allocated to common shareholders $ 40 $ 21 Undistributed earnings allocated to participating shareholders — — Undistributed earnings (loss) $ 40 $ 21 (2) Undistributed earnings are adjusted for the assumed distribution of dividends to the dilutive securities, which are described in (3) below, and then reallocated to participating securities. (3) Represents incremental shares of common stock from the (i) assumed exercise of stock options issued under Cabot’s equity incentive plans; and (ii) assumed issuance of shares to employees pursuant to the Company’s Deferred Compensation and Supplemental Retirement Plan. For the three months ended December 31, 2020 and 2019, 1,305,993 and 995,294 incremental shares of common stock, respectively, were excluded from the calculation of diluted earnings per share because the inclusion of these shares would have been antidilutive.

Restructuring

Restructuring	3 Months Ended
	Dec. 31, 2020
Restructuring And Related Activities [Abstract]
Restructuring	J. Restructuring Cabot’s restructuring activities were recorded in the Consolidated Statements of Operations in the three months ended December 31, 2020 and 2019 as follows: Three Months Ended December 31 2020 2019 (In millions) Cost of sales $ 3 $ 1 Selling and administrative expenses — 7 Total $ 3 $ 8 Details of all restructuring activities and the related reserves during the three months ended December 31, 2020 were as follows: Severance and Employee Benefits Environmental Remediation Non-cash Asset Impairment Other Total (In millions) Reserve at September 30, 2020 $ 5 $ 4 $ — $ — $ 9 Charges (gain) — — 2 1 3 Cost charged against assets — — (2 ) — (2 ) Cash paid (2 ) — — (1 ) (3 ) Reserve at December 31, 2020 3 4 — — 7 Cabot’s severance and employee benefit reserves and other closure related reserves are reflected in Accounts payable and accrued liabilities on the Company’s Consolidated Balance Sheets. Cabot’s environmental remediation reserves related to restructuring activities are reflected in Other liabilities on the Company’s Consolidated Balance Sheets. 2020 Reorganization During fiscal 2020, the Company initiated several actions that it believes will enable the Company to perform certain activities more cost-effectively. These actions primarily consist of the reorganization of Cabot’s leadership structure, the creation of a Global Business Services function and other operational efficiency initiatives. As part of the creation of the Global Business Services function, certain business service activities performed at Cabot’s North American business service center were consolidated into the Company’s European business service center. During the three months ended December 31, 2020 and 2019, the Company recorded charges of less than $1 million and $7 million, respectively, for these actions, primarily related to severance costs. The Company expects to record additional restructuring charges, primarily related to site demolition and severance costs associated with the Company’s other operational efficiency initiatives, of approximately $2 million throughout the rest of fiscal 2021 and $3 million thereafter. Cabot paid $2 million and $1 million related to these activities in the three months ended December 31, 2020 and 2019, respectively, and expects to pay approximately $3 million in the remainder of fiscal 2021 and $4 million thereafter. As of December 31, 2020, Cabot had $2 million of accrued severance charges in the Consolidated Balance Sheets related to these actions. As of December 31, 2020, the Company recorded total charges of $17 million and paid a total of $15 million in cash primarily related to these severance costs. Purification Solutions Transformation Plan In December 2018, the Company initiated a transformation plan to improve the long-term performance of the Purification Solutions segment. The purpose of the plan is to focus the business’s product portfolio, optimize its manufacturing assets, and streamline its organizational structure to support the new focus. During the three months ended December 31, 2020 and 2019, the Company recorded charges of $3 million and $1 million, respectively, under this plan related to actions affecting the business manufacturing facility in Marshall, Texas, which included charges associated with idling the activation kilns in September 2020. The Company expects to record additional restructuring charges, primarily related to decommissioning and severance costs, of approximately $2 million throughout the rest of fiscal 2021 and $1 million thereafter. During the three months ended December 31, 2020 and 2019, the Company paid $1 million and less than $1 million, respectively, primarily related to severance costs. The Company expects to pay approximately $2 million in the remainder of fiscal 2021 and $2 million thereafter primarily related to severance and decommissioning costs. As of December 31, 2020, Cabot had $1 million of accrued severance and other charges in the Consolidated Balance Sheets related to this plan. As of December 31, 2020, the Company recorded total charges of $14 million and paid a total of $10 million in cash for this plan primarily related to these severance costs.

Financial Instruments and Fair

Financial Instruments and Fair Value Measurements	3 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Financial Instruments and Fair Value Measurements	K. Financial Instruments and Fair Value Measurements The FASB authoritative guidance on fair value measurements defines fair value, provides a framework for measuring fair value, and requires certain disclosures about fair value measurements. The required disclosures focus on the inputs used to measure fair value. The guidance establishes the following hierarchy for categorizing these inputs: Level 1 — Quoted market prices in active markets for identical assets or liabilities Level 2 — Significant other observable inputs (e.g., quoted prices for similar items in active markets, quoted prices for identical or similar items in markets that are not active, inputs other than quoted prices that are observable such as interest rate and yield curves, and market-corroborated inputs) Level 3 — Significant unobservable inputs There were no transfers of financial assets or liabilities measured at fair value between Level 1 and Level 2 and there were no Level 3 investments during the first three months of either fiscal 2020 or 2019. At December 31, 2020 and September 30, 2020, Cabot had derivatives relating to foreign currency risks, including a net investment hedge and forward foreign currency contracts, carried at fair value. At December 31, 2020, the fair value of these derivatives was a net liability of $14 million and was included in Prepaid expenses and other current assets, Accounts payable and accrued liabilities, and Other liabilities on the Consolidated Balance Sheets. At September 30, 2020, the fair value of these derivatives was a net liability of $1 million and was included in Prepaid expenses and other current assets and Other liabilities on the Consolidated Balance Sheets. These derivatives are classified as Level 2 instruments within the fair value hierarchy as the fair value determination was based on observable inputs. At December 31, 2020 and September 30, 2020, the fair value of guaranteed investment contracts, included in Other assets on the Consolidated Balance Sheets, was $12 million and $11 million, respectively. Guaranteed investment contracts were classified as Level 2 instruments within the fair value hierarchy as the fair value determination was based on other observable inputs. At December 31, 2020 and September 30, 2020, the fair values of cash and cash equivalents, accounts and notes receivable, accounts payable and accrued liabilities, and short-term borrowings and variable rate debt approximated their carrying values due to the short-term nature of these instruments. The carrying value and fair value of the long-term fixed rate debt were $1.07 billion and $1.17 billion, respectively, as of December 31, 2020, and $1.08 billion and $1.18 billion, respectively, as of September 30, 2020. The fair values of Cabot’s fixed rate long-term debt are estimated based on comparable quoted market prices at the respective period ends. The carrying amounts of Cabot’s floating rate long-term debt and finance and operating lease obligations approximate their fair values. All such measurements are based on observable inputs and are classified as Level 2 within the fair value hierarchy. The valuation technique used is the discounted cash flow model.

Derivatives

Derivatives	3 Months Ended
	Dec. 31, 2020
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Derivatives	L. Derivatives Foreign Currency Risk Management Cabot’s international operations are subject to certain risks, including currency exchange rate fluctuations and government actions. Cabot endeavors to match the currency in which debt is issued to the currency of the Company’s major, stable cash receipts. In some situations, Cabot has issued debt denominated in U.S. dollars and then entered into cross-currency swaps that exchange the dollar principal and interest payments into Euro-denominated principal and interest payments. Additionally, the Company has foreign currency exposure arising from its net investments in foreign operations. Cabot may enter into cross-currency swaps to mitigate the impact of currency rate changes on the Company’s net investments. The Company also has foreign currency exposure arising from the denomination of monetary assets and liabilities in foreign currencies other than the functional currency of a given subsidiary as well as the risk that currency fluctuations could affect the dollar value of future cash flows generated in foreign currencies. Accordingly, Cabot uses short-term forward contracts to minimize the exposure to foreign currency risk. In certain situations where the Company has forecasted purchases under a long-term commitment or forecasted sales denominated in a foreign currency, Cabot may enter into appropriate financial instruments in accordance with the Company’s risk management policy to hedge future cash flow exposures. The following table provides details of the derivatives held as of December 31, 2020 and September 30, 2020 to manage foreign currency risk. Notional Amount Description Borrowing December 31, 2020 September 30, 2020 Hedge Designation Cross-Currency Swaps 3.4% Notes USD 250 million swapped to EUR 223 million USD 250 million swapped to EUR 223 million Net investment Forward Foreign Currency Contracts (1) N/A USD 39 million USD 54 million No designation (1) As of December 3 1 , 2020, Cabot’s forward foreign exchange contracts were denominated in Indonesian rupiah and Czech koruna. As of September 30, 20 20 , Cabot’s forward foreign exchange contracts were denominated in Canadian dollar, Indonesian rupiah and Czech koruna. At both December 31, 2020 and September 30, 2020 the fair value of these derivative instruments were a nominal amount. Accounting for Derivative Instruments and Hedging Activities The Company has cross-currency swaps with a notional amount of $250 million, which are designated as hedges of its net investments in certain Euro-denominated subsidiaries. Cash settlements occur semi-annually on March 15 th th The following table summarizes the impact of the cross-currency swaps to AOCI and the Consolidated Statements of Operations: Three Months Ended December 31 2020 2019 2020 2019 2020 2019 Description Gain/(Loss) Recognized in AOCI (Gain)/Loss Reclassified from AOCI into Interest Expense in the Consolidated Statements of Operations (Gain)/Loss Recognized in Interest Expense in the Consolidated Statements of Operations (Amount Excluded from Effectiveness Testing) (In millions) Cross-currency swaps $ (13 ) $ (4 ) $ (1 ) $ (1 ) $ — $ —

Financial Information by Segmen

Financial Information by Segment	3 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Financial Information by Segment	M. 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”), who is Cabot’s President and Chief Executive Officer, to make decisions about resources to be allocated to the segment and assess its performance; and (iii) it has available discrete financial information. The Company has determined that all of its businesses are operating segments. The CODM reviews financial information at the operating segment level to allocate resources and to assess the operating results and financial performance for each operating segment. Operating segments are aggregated into a reportable segment if the operating segments are determined to have similar economic characteristics and if the operating segments are similar in the following areas: (i) nature of products and services; (ii) nature of production processes; (iii) type or class of customer for their products and services; (iv) methods used to distribute the products or provide services; and (v) if applicable, the nature of the regulatory environment. The Company has three reportable segments: Reinforcement Materials, Performance Chemicals, and Purification Solutions. The Reinforcement Materials segment consists of the rubber blacks and elastomer composites product lines. The Performance Chemicals segment combines the specialty carbons, fumed metal oxides and aerogel product lines into the Performance Additives business, and combines the specialty compounds and inkjet colorants product lines into the Formulated Solutions business. These businesses are similar in terms of economic characteristics, nature of products, processes, customer class and product distribution methods, and, therefore, have been aggregated into one reportable segment. The net sales from each of these businesses for the three months ended December 31, 2020 and 2019 were as follows: Three Months Ended December 31 2020 2019 (In millions) Performance Additives $ 184 $ 170 Formulated Solutions 83 72 Total Performance Chemicals $ 267 $ 242 The Purification Solutions segment consists of the Company’s activated carbon business. Income (loss) before income taxes (“Segment EBIT”) is presented for each reportable segment in the table below. Segment EBIT excludes Interest expense, general unallocated income (expense), unallocated corporate costs, and certain items, meaning items management does not consider representative of on-going operating segment results. In addition, Segment EBIT includes Equity in earnings of affiliated companies, net of tax, the full operating results of a contractual joint venture in Purification Solutions, royalties, Net income attributable to noncontrolling interests, net of tax, and discounting charges for certain Notes receivable. Financial information by reportable segment is as follows: Reinforcement Materials Performance Chemicals Purification Solutions Segment Total Unallocated and Other (1) Consolidated Total (In millions) Three Months Ended December 31, 2020 Revenues from external customers (2) $ 375 $ 267 $ 59 $ 701 $ 45 $ 746 Income (loss) before income taxes (3) $ 88 $ 54 $ (2 ) $ 140 $ (41 ) $ 99 Three Months Ended December 31, 2019 Revenues from external customers (2) $ 379 $ 242 $ 59 $ 680 $ 47 $ 727 Income (loss) before income taxes (3) $ 47 $ 41 $ (2 ) $ 86 $ (36 ) $ 50 ( 1 ) ( 2 ) Consolidated Total Revenues from external customers reconciles to Net sales and other operating revenues on the Consolidated Statements of Operations. Three Months Ended December 31 2020 2019 (In millions) Royalties, the impact of unearned revenue, the removal of 100% of the sales of an equity method affiliate and discounting charges for certain notes receivable $ (5 ) $ (1 ) Shipping and handling fees 33 31 By-product sales 17 17 Total $ 45 $ 47 ( 3 ) Consolidated Total Income (loss) before income taxes Three Months Ended December 31 2020 2019 (In millions) Interest expense $ (12 ) $ (14 ) Certain items (a) Employee benefit plan settlement and other charges (Note D) (6 ) (2 ) Global restructuring activities (Note J) (3 ) (8 ) Acquisition and integration-related charges (1 ) (1 ) Legal and environmental matters and reserves — 1 Other (1 ) (1 ) Total certain items, pre-tax (11 ) (11 ) Unallocated corporate costs (b) (13 ) (10 ) General unallocated income (expense) (c) (5 ) (1 ) Less: Equity in earnings of affiliated companies, net of tax (d) — — Total $ (41 ) $ (36 ) (a) Certain items are (b) Unallocated corporate costs are costs that are not controlled by the segments and primarily benefit corporate interests. (c) General unallocated income (expense) consists of gains (losses) arising from foreign currency transactions, net of other foreign currency risk management activities, Interest and dividend income, the profit or loss related to the corporate adjustment for unearned revenue, the impact of including the full operating results of a contractual joint venture in Purification Solutions Segment EBIT and unrealized holding gains (losses) for equity securities. (d) Equity in earnings of affiliated companies, net of tax, is included in Segment EBIT and is removed in Unallocated and other to reconcile to Income (loss) from operations before income taxes and equity in earnings from affiliated companies. The Company’s segments operate globally. In addition to presenting Revenue from external customers by reportable segment, the following tables further disaggregate Revenues from external customers by geographic region. Three Months Ended December 31, 2020 Reinforcement Materials Performance Chemicals Purification Solutions Consolidated Total (In millions) Americas $ 149 $ 69 $ 25 $ 243 Asia Pacific 155 118 9 282 Europe, Middle East and Africa 71 80 25 176 Segment revenues from external customers 375 267 59 701 Unallocated and other 45 Net sales and other operating revenues $ 746 Three Months Ended December 31, 2019 Reinforcement Materials Performance Chemicals Purification Solutions Consolidated Total (In millions) Americas $ 141 $ 76 $ 26 $ 243 Asia Pacific 170 94 9 273 Europe, Middle East and Africa 68 72 24 164 Segment revenues from external customers 379 242 59 680 Unallocated and other 47 Net sales and other operating revenues $ 727

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	3 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards In June 2016, the FASB issued a new standard on measurement of credit losses. The standard introduces a new "expected loss" impairment model that applies to most financial assets measured at amortized cost and certain other instruments, including trade and other receivables and other financial assets. Entities are required to estimate expected credit losses over the life of financial assets and record an allowance against the assets’ amortized cost basis to present them at the amount expected to be collected. The Company adopted this standard on October 1, 2020. The adoption of this standard did not materially impact the Company’s consolidated financial statements.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In March 2020, the FASB issued a new standard on Reference Rate Reform, which provides temporary optional expedients and exceptions to the existing guidance on contract modifications and hedge accounting to ease the financial reporting burdens related to the expected market transition from the London Interbank Offered Rate ("LIBOR") and other interbank offered rates to alternative reference rates. The standard was effective upon issuance and may generally be applied through December 31, 2022 to any new or amended contracts, hedging relationships, and other transactions that reference LIBOR. The Company is currently evaluating the timing of adoption and the impact of the adoption of this standard on its consolidated financial statements. In December 2019, the FASB issued a new standard Simplifying the Accounting for Income Taxes. The new guidance simplifies the accounting for income taxes by removing several exceptions in the current standard and adding guidance to reduce complexity in certain areas. The new standard is effective for fiscal years beginning after December 15, 2020 and early adoption is permitted. The Company is currently evaluating the timing of adoption and the impact of the adoption of this standard on its consolidated financial statements.

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	3 Months Ended
	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
Net Periodic Defined Benefit Pension Costs	Net periodic defined benefit pension costs include the following: Three Months Ended December 31 2020 2019 Pension Benefits U.S. Foreign U.S. Foreign (In millions) Service cost $ — $ 1 $ — $ 1 Interest cost — 1 1 1 Expected return on plan assets — (2 ) (1 ) (2 ) Amortization of actuarial loss — 1 — 1 Settlement charge 6 — — — Net periodic benefit (credit) cost $ 6 $ 1 $ — $ 1

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	3 Months Ended
	Dec. 31, 2020
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 three months ended December 31, 2020 are as follows: Reinforcement Materials Performance Chemicals Total (In millions) Balance at September 30, 2020 $ 46 $ 88 $ 134 Foreign currency impact 4 4 8 Balance at December 31, 2020 $ 50 $ 92 $ 142
Schedule of Intangible Assets	The following table provides information regarding the Company’s intangible assets: December 31, 2020 September 30, 2020 Gross Carrying Value Accumulated Amortization Net Intangible Assets Gross Carrying Value Accumulated Amortization Net Intangible Assets (In millions) Intangible assets with finite lives Developed technologies $ 63 $ (9 ) $ 54 $ 60 $ (8 ) $ 52 Trademarks 11 (1 ) 10 11 (1 ) 10 Customer relationships 61 (18 ) 43 56 (15 ) 41 Total intangible assets (1) $ 135 $ (28 ) $ 107 $ 127 $ (24 ) $ 103 (1) The increase in value of Total intangible assets as of December 31, 2020 compared to September 30, 2020 was driven by the impact of foreign currency translation.

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Dec. 31, 2020
Equity [Abstract]
Changes in Each Component of AOCI, Net of Tax	Changes in each component of AOCI, net of tax, were as follows: Currency Translation Adjustment Pension and Other Postretirement Benefit Liability Adjustments Total (In millions) Balance at September 30, 2020, attributable to Cabot Corporation $ (307 ) $ (44 ) $ (351 ) Other comprehensive income (loss) before reclassifications 94 (1 ) 93 Amounts reclassified from AOCI (1 ) 4 3 Less: Other comprehensive income (loss) attributable to noncontrolling interests 7 — 7 Balance at December 31, 2020, attributable to Cabot Corporation $ (221 ) $ (41 ) $ (262 )
Amounts Reclassified Out of AOCI	The amounts reclassified out of AOCI and into the Consolidated Statements of Operations in each of the three months ended December 31, 2020 and 2019 were as follows: Affected Line Item in the Consolidated Three Months Ended December 31 Statements of Operations 2020 2019 (In millions) Derivatives: net investment hedges (Gains) losses reclassified to interest expense Interest expense (Note L) $ (1 ) $ (1 ) Pension and other postretirement Amortization of actuarial losses and prior service cost (credit) Net Periodic Benefit Cost (Note D) 1 1 Settlement charge Net Periodic Benefit Cost (Note D) 6 — Total before tax 6 — Tax impact Provision (benefit) for income taxes (3 ) — Total after tax $ 3 $ —

Income Tax (Tables)

Income Tax (Tables)	3 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Effective Tax Rate	Effective Tax Rate Three Months Ended December 31 2020 2019 (Dollars in millions) (Provision) benefit for income taxes $ (29 ) $ (4 ) Effective tax rate 29 % 7 %

Earnings Per Share (Tables)

Earnings Per Share (Tables)	3 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Components of Basic and Diluted Earnings (Loss) Per Common Share (EPS)	The following tables summarize the components of the basic and diluted earnings (loss) per common share (“EPS”) computations: Three Months Ended December 31 2020 2019 (In millions, except per share amounts) Basic EPS: Net income (loss) attributable to Cabot Corporation $ 60 $ 41 Less: Dividends and dividend equivalents to participating securities — — Earnings (loss) allocated to common shareholders (numerator) $ 60 $ 41 Weighted average common shares and participating securities outstanding 57.2 57.7 Less: Participating securities (1) 0.7 0.8 Adjusted weighted average common shares (denominator) 56.5 56.9 Earnings (loss) per common share - basic: $ 1.06 $ 0.71 Diluted EPS: Earnings (loss) allocated to common shareholders $ 60 $ 41 Plus: Earnings allocated to participating securities — — Less: Adjusted earnings allocated to participating securities (2) — — Earnings (loss) allocated to common shareholders (numerator) $ 60 $ 41 Adjusted weighted average common shares outstanding 56.5 56.9 Effect of dilutive securities: Common shares issuable (3) 0.1 0.1 Adjusted weighted average common shares (denominator) 56.6 57.0 Earnings (loss) per common share - diluted: $ 1.06 $ 0.70 (1) Participating securities consist of shares underlying all outstanding and achieved performance-based restricted stock units and all unvested time-based restricted stock units. The holders of these units are entitled to receive dividend equivalents payable in cash to the extent dividends are paid on the Company’s outstanding common stock and equal in value to the dividends that would have been paid in respect of the shares underlying such units.
Calculation of Undistributed Earnings	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 December 31 2020 2019 (In millions) Calculation of undistributed earnings (loss): Net income (loss) attributable to Cabot Corporation $ 60 $ 41 Less: Dividends declared on common stock 20 20 Less: Dividends declared on participating securities — — Undistributed earnings (loss) $ 40 $ 21 Allocation of undistributed earnings (loss): Undistributed earnings (loss) allocated to common shareholders $ 40 $ 21 Undistributed earnings allocated to participating shareholders — — Undistributed earnings (loss) $ 40 $ 21 (2) Undistributed earnings are adjusted for the assumed distribution of dividends to the dilutive securities, which are described in (3) below, and then reallocated to participating securities. (3) Represents incremental shares of common stock from the (i) assumed exercise of stock options issued under Cabot’s equity incentive plans; and (ii) assumed issuance of shares to employees pursuant to the Company’s Deferred Compensation and Supplemental Retirement Plan. For the three months ended December 31, 2020 and 2019, 1,305,993 and 995,294 incremental shares of common stock, respectively, were excluded from the calculation of diluted earnings per share because the inclusion of these shares would have been antidilutive.

Restructuring (Tables)

Restructuring (Tables)	3 Months Ended
	Dec. 31, 2020
Restructuring And Related Activities [Abstract]
Recorded Restructuring Activities	Cabot’s restructuring activities were recorded in the Consolidated Statements of Operations in the three months ended December 31, 2020 and 2019 as follows: Three Months Ended December 31 2020 2019 (In millions) Cost of sales $ 3 $ 1 Selling and administrative expenses — 7 Total $ 3 $ 8
Restructuring Activities and Related Reserves	Details of all restructuring activities and the related reserves during the three months ended December 31, 2020 were as follows: Severance and Employee Benefits Environmental Remediation Non-cash Asset Impairment Other Total (In millions) Reserve at September 30, 2020 $ 5 $ 4 $ — $ — $ 9 Charges (gain) — — 2 1 3 Cost charged against assets — — (2 ) — (2 ) Cash paid (2 ) — — (1 ) (3 ) Reserve at December 31, 2020 3 4 — — 7

Derivatives (Tables)

Derivatives (Tables)	3 Months Ended
	Dec. 31, 2020
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Details of Derivatives Held to Manage Foreign Currency Risk	The following table provides details of the derivatives held as of December 31, 2020 and September 30, 2020 to manage foreign currency risk. Notional Amount Description Borrowing December 31, 2020 September 30, 2020 Hedge Designation Cross-Currency Swaps 3.4% Notes USD 250 million swapped to EUR 223 million USD 250 million swapped to EUR 223 million Net investment Forward Foreign Currency Contracts (1) N/A USD 39 million USD 54 million No designation (1) As of December 3 1 , 2020, Cabot’s forward foreign exchange contracts were denominated in Indonesian rupiah and Czech koruna. As of September 30, 20 20 , Cabot’s forward foreign exchange contracts were denominated in Canadian dollar, Indonesian rupiah and Czech koruna. At both December 31, 2020 and September 30, 2020 the fair value of these derivative instruments were a nominal amount.
Summary Impact of Cross-currency Swaps to AOCI and Consolidated Statements of Operations	The following table summarizes the impact of the cross-currency swaps to AOCI and the Consolidated Statements of Operations: Three Months Ended December 31 2020 2019 2020 2019 2020 2019 Description Gain/(Loss) Recognized in AOCI (Gain)/Loss Reclassified from AOCI into Interest Expense in the Consolidated Statements of Operations (Gain)/Loss Recognized in Interest Expense in the Consolidated Statements of Operations (Amount Excluded from Effectiveness Testing) (In millions) Cross-currency swaps $ (13 ) $ (4 ) $ (1 ) $ (1 ) $ — $ —

Financial Information by Segm_2

Financial Information by Segment (Tables)	3 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Schedule of Performance Segment	The net sales from each of these businesses for the three months ended December 31, 2020 and 2019 were as follows: Three Months Ended December 31 2020 2019 (In millions) Performance Additives $ 184 $ 170 Formulated Solutions 83 72 Total Performance Chemicals $ 267 $ 242
Financial Information by Reportable Segment	Financial information by reportable segment is as follows: Reinforcement Materials Performance Chemicals Purification Solutions Segment Total Unallocated and Other (1) Consolidated Total (In millions) Three Months Ended December 31, 2020 Revenues from external customers (2) $ 375 $ 267 $ 59 $ 701 $ 45 $ 746 Income (loss) before income taxes (3) $ 88 $ 54 $ (2 ) $ 140 $ (41 ) $ 99 Three Months Ended December 31, 2019 Revenues from external customers (2) $ 379 $ 242 $ 59 $ 680 $ 47 $ 727 Income (loss) before income taxes (3) $ 47 $ 41 $ (2 ) $ 86 $ (36 ) $ 50 ( 1 ) ( 2 ) Consolidated Total Revenues from external customers reconciles to Net sales and other operating revenues on the Consolidated Statements of Operations. Three Months Ended December 31 2020 2019 (In millions) Royalties, the impact of unearned revenue, the removal of 100% of the sales of an equity method affiliate and discounting charges for certain notes receivable $ (5 ) $ (1 ) Shipping and handling fees 33 31 By-product sales 17 17 Total $ 45 $ 47 ( 3 ) Consolidated Total Income (loss) before income taxes Three Months Ended December 31 2020 2019 (In millions) Interest expense $ (12 ) $ (14 ) Certain items (a) Employee benefit plan settlement and other charges (Note D) (6 ) (2 ) Global restructuring activities (Note J) (3 ) (8 ) Acquisition and integration-related charges (1 ) (1 ) Legal and environmental matters and reserves — 1 Other (1 ) (1 ) Total certain items, pre-tax (11 ) (11 ) Unallocated corporate costs (b) (13 ) (10 ) General unallocated income (expense) (c) (5 ) (1 ) Less: Equity in earnings of affiliated companies, net of tax (d) — — Total $ (41 ) $ (36 ) (a) Certain items are (b) Unallocated corporate costs are costs that are not controlled by the segments and primarily benefit corporate interests. (c) General unallocated income (expense) consists of gains (losses) arising from foreign currency transactions, net of other foreign currency risk management activities, Interest and dividend income, the profit or loss related to the corporate adjustment for unearned revenue, the impact of including the full operating results of a contractual joint venture in Purification Solutions Segment EBIT and unrealized holding gains (losses) for equity securities. (d) Equity in earnings of affiliated companies, net of tax, is included in Segment EBIT and is removed in Unallocated and other to reconcile to Income (loss) from operations before income taxes and equity in earnings from affiliated companies.
Revenues from External Customers by Geographic Region	The Company’s segments operate globally. In addition to presenting Revenue from external customers by reportable segment, the following tables further disaggregate Revenues from external customers by geographic region. Three Months Ended December 31, 2020 Reinforcement Materials Performance Chemicals Purification Solutions Consolidated Total (In millions) Americas $ 149 $ 69 $ 25 $ 243 Asia Pacific 155 118 9 282 Europe, Middle East and Africa 71 80 25 176 Segment revenues from external customers 375 267 59 701 Unallocated and other 45 Net sales and other operating revenues $ 746 Three Months Ended December 31, 2019 Reinforcement Materials Performance Chemicals Purification Solutions Consolidated Total (In millions) Americas $ 141 $ 76 $ 26 $ 243 Asia Pacific 170 94 9 273 Europe, Middle East and Africa 68 72 24 164 Segment revenues from external customers 379 242 59 680 Unallocated and other 47 Net sales and other operating revenues $ 727

Acquisitions - Additional Infor

Acquisitions - Additional Information (Detail) - USD ($) $ in Millions	Apr. 01, 2020	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Businesses acquisition, net of cash acquired				$ 8
Assumed debt repaid			$ 66	$ 48
Shenzhen Sanshun Nano New Materials Co., Ltd [Member]
Business Acquisition [Line Items]
Business acquisition, purchase price	$ 100
Business acquisition, cash consideration	84
Businesses acquisition, net of cash acquired	1
Business acquisition, assumed debt	13
Assumed debt repaid		$ 13
Business combination future contingent consideration milestone payment	$ 3

Employee Benefit Plans - Net Pe

Employee Benefit Plans - Net Periodic Defined Benefit Pension Costs (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement charge	$ 6	$ 3
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost			$ 1
Expected return on plan assets			(1)
Settlement charge	6
Net periodic benefit (credit) cost	6
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1		1
Interest cost	1		1
Expected return on plan assets	(2)		(2)
Amortization of actuarial loss	1		1
Net periodic benefit (credit) cost	$ 1		$ 1

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) - USD ($)	3 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement charge	$ 6,000,000	$ 3,000,000
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Settlement Gain (Loss), Statement of Income or Comprehensive Income [Extensible List]	us-gaap:OtherNonoperatingIncomeExpenseMember	us-gaap:OtherNonoperatingIncomeExpenseMember
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Other postretirement benefit costs (gains)	$ 1,000,000		$ 1,000,000

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Schedule of Goodwill Balances (Detail) $ in Millions	3 Months Ended
	Dec. 31, 2020USD ($)
Goodwill And Intangible Assets [Line Items]
Beginning balance	$ 134
Foreign currency impact	8
Ending balance	142
Reinforcement Materials [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	46
Foreign currency impact	4
Ending balance	50
Performance Chemicals [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	88
Foreign currency impact	4
Ending balance	$ 92

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Schedule of Intangible Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Sep. 30, 2020
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	$ 135	$ 127
Accumulated Amortization	(28)	(24)
Net Intangible Assets, finite lives	107	103
Developed Technologies [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	63	60
Accumulated Amortization	(9)	(8)
Net Intangible Assets, finite lives	54	52
Trademarks [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	11	11
Accumulated Amortization	(1)	(1)
Net Intangible Assets, finite lives	10	10
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	61	56
Accumulated Amortization	(18)	(15)
Net Intangible Assets, finite lives	$ 43	$ 41

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Goodwill And Intangible Assets [Line Items]
Amortization expense estimated for year one	$ 8
Amortization expense estimated for year two	8
Amortization expense estimated for year three	8
Amortization expense estimated for year four	8
Amortization expense estimated for year five	8
Cost of Sales, Selling and Administrative Expenses and Research and Technical Expenses [Member]
Goodwill And Intangible Assets [Line Items]
Amortization of intangible assets	$ 2	$ 1
Minimum [Member]
Goodwill And Intangible Assets [Line Items]
Useful life of intangible assets	10 years
Maximum [Member]
Goodwill And Intangible Assets [Line Items]
Useful life of intangible assets	25 years
Weighted Average [Member]
Goodwill And Intangible Assets [Line Items]
Useful life of intangible assets	18 years

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) - Changes in Each Component of AOCI, Net of Tax (Detail) $ in Millions	3 Months Ended
	Dec. 31, 2020USD ($)
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 814
Ending Balance	962
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(307)
Other comprehensive income (loss) before reclassifications	94
Amounts reclassified from AOCI	(1)
Less: Other comprehensive income (loss) attributable to noncontrolling interests	7
Ending Balance	(221)
Pension and Other Postretirement Benefit Liability Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(44)
Other comprehensive income (loss) before reclassifications	(1)
Amounts reclassified from AOCI	4
Ending Balance	(41)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(351)
Other comprehensive income (loss) before reclassifications	93
Amounts reclassified from AOCI	3
Less: Other comprehensive income (loss) attributable to noncontrolling interests	7
Ending Balance	$ (262)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified Out of AOCI (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
(Gains) Losses Reclassified to Interest Expense [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (1)	$ (1)
Amortization of Actuarial Losses and Prior Service Cost (Credit) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	1	$ 1
Settlement Charge [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	6
Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	6
Tax impact	(3)
Total after tax	$ 3

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - Respirator Liabilities [Member] - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2020
Loss Contingencies [Line Items]
Respirator liability			$ 65.2
Settlement amount		$ 32.6
Description of pending claims	The Company paid $32.6 million of the settlement during the third quarter of fiscal 2020 and the remaining $32.6 million in the first quarter of fiscal 2021.
Respirator reserve	$ 23			$ 24
Selling and Administrative Expenses [Member]
Loss Contingencies [Line Items]
Respirator charge			$ 50
Accounts Payable and Accrued Liabilities [Member]
Loss Contingencies [Line Items]
Settlement amount	$ 32.6

Income Tax - Effective Tax Rate

Income Tax - Effective Tax Rate (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
(Provision) benefit for income taxes	$ (29)	$ (4)
Effective tax rate	29.00%	7.00%

Income Tax - Additional Informa

Income Tax - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Taxes [Line Items]
Net discrete tax (benefits) expense related to tax settlements	$ 2	$ (10)
Uncertain tax positions from expirations of statute of limitations	$ 1	6
Accrued uncertain tax position for potential settlement		$ 2
Earliest Tax Year [Member] | United States Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Tax years remain subject to examination	2017
Latest Tax Year [Member] | United States Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Tax years remain subject to examination	2019
State Tax Authorities [Member] | Earliest Tax Year [Member]
Income Taxes [Line Items]
Tax years remain subject to examination	2005
State Tax Authorities [Member] | Latest Tax Year [Member]
Income Taxes [Line Items]
Tax years remain subject to examination	2019
Non-U.S. Jurisdictions [Member] | Earliest Tax Year [Member]
Income Taxes [Line Items]
Tax years remain subject to examination	2003
Non-U.S. Jurisdictions [Member] | Latest Tax Year [Member]
Income Taxes [Line Items]
Tax years remain subject to examination	2020

Earnings Per Share - Components

Earnings Per Share - Components of Basic and Diluted Earnings (Loss) Per Common Share (EPS) (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Basic EPS:
Net income (loss) attributable to Cabot Corporation	$ 60	$ 41
Earnings (loss) allocated to common shareholders (numerator)	$ 60	$ 41
Weighted average common shares and participating securities outstanding	57.2	57.7
Less: Participating securities	0.7	0.8
Adjusted weighted average common shares (denominator)	56.5	56.9
Earnings (loss) per common share - basic:	$ 1.06	$ 0.71
Diluted EPS:
Earnings (loss) allocated to common shareholders	$ 60	$ 41
Earnings (loss) allocated to common shareholders (numerator)	$ 60	$ 41
Adjusted weighted average common shares outstanding	56.5	56.9
Common shares issuable	0.1	0.1
Adjusted weighted average common shares (denominator)	56.6	57
Earnings (loss) per common share - diluted:	$ 1.06	$ 0.70

Earnings Per Share - Calculatio

Earnings Per Share - Calculation of Undistributed Earnings (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Net income (loss) attributable to Cabot Corporation	$ 60	$ 41
Less: Dividends declared on common stock	20	20
Undistributed earnings (loss)	40	21
Undistributed earnings (loss) allocated to common shareholders	$ 40	$ 21

Earnings Per Share - Componen_2

Earnings Per Share - Components of Basic and Diluted Earnings (Loss) Per Common Share (EPS) (Parenthetical) (Detail) - shares	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share	1,305,993	995,294

Restructuring - Recorded Restru

Restructuring - Recorded Restructuring Activities (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Restructuring Cost And Reserve [Line Items]
Restructuring reserve, period expense	$ 3	$ 8
Cost of Sales [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring reserve, period expense	$ 3	1
Selling and Administrative Expenses [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring reserve, period expense		$ 7

Restructuring - Restructuring A

Restructuring - Restructuring Activities and Related Reserves (Detail) $ in Millions	3 Months Ended
	Dec. 31, 2020USD ($)
Restructuring Cost And Reserve [Line Items]
Reserve balance	$ 9
Charges (gain)	3
Cost charged against assets	(2)
Cash paid	(3)
Reserve balance	7
Severance and Employee Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	5
Cash paid	(2)
Reserve balance	3
Non-cash Asset Impairment [Member]
Restructuring Cost And Reserve [Line Items]
Charges (gain)	2
Cost charged against assets	(2)
Other [Member]
Restructuring Cost And Reserve [Line Items]
Charges (gain)	1
Cash paid	(1)
Environmental Remediation [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	4
Reserve balance	$ 4

Restructuring - Additional Info

Restructuring - Additional Information (Detail) - USD ($)	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Restructuring Cost And Reserve [Line Items]
Restructuring charges	$ 3,000,000
2020 Reorganization [Member]
Restructuring Cost And Reserve [Line Items]
Severance costs		$ 7,000,000
Restructuring charges expected throughout rest of 2021 related to site demolition and severance costs	2,000,000
Restructuring charges expected thereafter fiscal year related to site demolition and severance costs	3,000,000
Restructuring cash payments of fiscal year	2,000,000	1,000,000
Restructuring cash payments through the reminder of fiscal 2021	3,000,000
Restructuring future cash payments thereafter fiscal year	4,000,000
Accrued severance charges	2,000,000
Restructuring charges	17,000,000
2020 Reorganization [Member] | Severance and Employee Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Payment for restructuring	15,000,000
2020 Reorganization [Member] | Maximum [Member]
Restructuring Cost And Reserve [Line Items]
Severance costs	1,000,000
Purification Solutions Transformation Plan [Member]
Restructuring Cost And Reserve [Line Items]
Severance costs	1,000,000
Restructuring cash payments through the reminder of fiscal 2021	2,000,000
Restructuring future cash payments thereafter fiscal year	2,000,000
Accrued severance charges	1,000,000
Restructuring charges	14,000,000
Restructuring charges expected throughout rest of 2021 related to decommissioning and severance costs	2,000,000
Restructuring charges expected thereafter fiscal year related to decommissioning and severance costs	1,000,000
Purification Solutions Transformation Plan [Member] | Manufacturing Facility [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring charges	3,000,000	1,000,000
Purification Solutions Transformation Plan [Member] | Severance and Employee Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Payment for restructuring	$ 10,000,000
Purification Solutions Transformation Plan [Member] | Maximum [Member]
Restructuring Cost And Reserve [Line Items]
Severance costs		$ 1,000,000

Financial Instruments and Fai_2

Financial Instruments and Fair Value Measurements - Additional Information (Detail) - USD ($)	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
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	1,170,000,000		$ 1,180,000,000
Fixed Rate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of long-term debt	1,070,000,000		1,080,000,000
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		11,000,000
Significant Observable Inputs (Level 2) [Member] | Foreign Currency Risks [Member] | Prepaid Expenses and Other Current Assets and Other Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets (liabilities), at fair Value, net	$ (14,000,000)		$ (1,000,000)

Derivatives - Details of Deriva

Derivatives - Details of Derivatives Held to Manage Foreign Currency Risk (Detail)		Dec. 31, 2020USD ($)	Dec. 31, 2020EUR (€)	Sep. 30, 2020USD ($)	Sep. 30, 2020EUR (€)
Net Investment Hedge [Member] | Cross Currency Swaps [Member]
Derivative [Line Items]
Notional Amount		$ 250,000,000
Net Investment Hedge [Member] | 3.4% Notes [Member] | Cross Currency Swaps [Member]
Derivative [Line Items]
Notional Amount		$ 250,000,000	€ 223,000,000	$ 250,000,000	€ 223,000,000
Net Investment Hedge [Member] | 3.4% Notes [Member] | Fixed Rate Debt [Member] | Cross Currency Swaps [Member]
Derivative [Line Items]
Interest rate on borrowing		3.40%	3.40%	3.40%	3.40%
Not Designated as Hedging Instrument [Member] | Forward Foreign Currency Contracts [Member]
Derivative [Line Items]
Notional Amount	[1]	$ 39,000,000		$ 54,000,000
[1]	As of December 3 1 , 2020, Cabot’s forward foreign exchange contracts were denominated in Indonesian rupiah and Czech koruna. As of September 30, 20 20 , Cabot’s forward foreign exchange contracts were denominated in Canadian dollar, Indonesian rupiah and Czech koruna. At both December 31, 2020 and September 30, 2020 the fair value of these derivative instruments were a nominal amount.

Derivatives - Additional Inform

Derivatives - Additional Information (Detail) - Cross Currency Swaps [Member] - USD ($)	3 Months Ended
	Dec. 31, 2020	Sep. 30, 2020
Derivative [Line Items]
Fair value of swaps, net liability	$ 14,000,000	$ 1,000,000
Net Investment Hedge [Member]
Derivative [Line Items]
Notional Amount	250,000,000
Cumulative gain (loss) related to swaps	$ (12,000,000)	$ 2,000,000
Net Investment Hedge [Member] | Fixed Rate Debt [Member]
Derivative [Line Items]
Derivative Instruments Frequency of Cash Settlements	semi-annually

Derivatives - Summary Impact of

Derivatives - Summary Impact of Cross-currency Swaps to AOCI and Consolidated Statements of Operations (Detail) - Cross Currency Swaps [Member] - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Derivative Instruments Gain Loss [Line Items]
Gain/(Loss) Recognized in AOCI	$ (13)	$ (4)
(Gain)/Loss Reclassified from AOCI into Interest Expense in the Consolidated Statements of Operations	$ (1)	$ (1)

Financial Information by Segm_3

Financial Information by Segment - Additional Information (Detail)	3 Months Ended
	Dec. 31, 2020Segment
Segment Reporting Information [Line Items]
Number of business reportable segments	3
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Number of business reportable segments	1

Financial Information by Segm_4

Financial Information by Segment - Schedule of Performance Segment (Detail) - Performance Chemicals [Member] - Operating Segments [Member] - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net sales	$ 267	$ 242
Performance Additives [Member]
Segment Reporting Information [Line Items]
Net sales	184	170
Formulated Solutions [Member]
Segment Reporting Information [Line Items]
Net sales	$ 83	$ 72

Financial Information by Segm_5

Financial Information by Segment - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues from external customers	$ 746	$ 727
Income (loss) before income taxes	99	50
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	701	680
Income (loss) before income taxes	140	86
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	45	47
Income (loss) before income taxes	(41)	(36)
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	375	379
Income (loss) before income taxes	88	47
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	267	242
Income (loss) before income taxes	54	41
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	59	59
Income (loss) before income taxes	$ (2)	$ (2)

Financial Information by Segm_6

Financial Information by Segment - Financial Information by Reportable Segment (Parenthetical) (Detail)	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting [Abstract]
Percentage of sale of an equity method affiliate	100.00%	100.00%

Financial Information by Segm_7

Financial Information by Segment - Sales of Equity Method Affiliate and Discounting Charges for Certain Notes Receivable and By-product Revenue (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Revenues from external customers	$ 746	$ 727
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	45	47
Unallocated and Other [Member] | Royalties, the Impact of Unearned Revenue, the Removal of 100% of the Sales of an Equity Method Affiliate and Discounting Charges for Certain Notes Receivable [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	(5)	(1)
Unallocated and Other [Member] | Shipping and Handling Costs [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	33	31
Unallocated and Other [Member] | By-product Sales [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	$ 17	$ 17

Financial Information by Segm_8

Financial Information by Segment - Sales of Equity Method Affiliate and Discounting Charges for Certain Notes Receivable and By-product Revenue (Parenthetical) (Detail)	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting [Abstract]
Percentage of sale of an equity method affiliate	100.00%	100.00%

Financial Information by Segm_9

Financial Information by Segment - Schedule of Income (Loss) from Continuing Operations before Income Taxes and Equity in Earnings of Affiliated Companies for Unallocated and Other (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Interest expense	$ (12)	$ (14)
Global restructuring activities	(3)	(8)
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Interest expense	(12)	(14)
Unallocated corporate costs	(13)	(10)
General unallocated income (expense)	(5)	(1)
Income from continuing operations before income taxes and equity in earnings of affiliated companies	(41)	(36)
Certain Items [Member]
Segment Reporting Information [Line Items]
Employee benefit plan settlement and other charges	(6)	(2)
Global restructuring activities	(3)	(8)
Acquisition and integration-related charges	(1)	(1)
Legal and environmental matters and reserves		1
Other	(1)	(1)
Total certain items, pre-tax	$ (11)	$ (11)

Financial Information by Seg_10

Financial Information by Segment - Revenue from External Customers by Geographic Region (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 746	$ 727
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	701	680
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	45	47
Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	243	243
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	282	273
Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	176	164
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	375	379
Reinforcement Materials [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	149	141
Reinforcement Materials [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	155	170
Reinforcement Materials [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	71	68
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	267	242
Performance Chemicals [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	69	76
Performance Chemicals [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	118	94
Performance Chemicals [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	80	72
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	59	59
Purification Solutions [Member] | Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	25	26
Purification Solutions [Member] | Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	9	9
Purification Solutions [Member] | Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 25	$ 24