Cabot (CBT) 10-K 25 Nov 20 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2020	Nov. 20, 2020	Mar. 31, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Sep. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Trading Symbol	CBT
Entity Registrant Name	Cabot Corporation
Entity Central Index Key	0000016040
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		56,600,026
Entity Public Float			$ 1,467,794,829
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Interactive Data Current	Yes
Entity File Number	1-5667
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-2271897
Entity Address, Address Line One	Two Seaport Lane
Entity Address, Address Line Two	Suite 1400
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02210
City Area Code	617
Local Phone Number	345-0100
Document Annual Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, $1 par value per share
Security Exchange Name	NYSE

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Net sales and other operating revenues	$ 2,614	$ 3,337	$ 3,242
Cost of sales	2,114	2,652	2,470
Gross profit	500	685	772
Selling and administrative expenses	292	290	308
Research and technical expenses	57	60	66
Purification Solutions long-lived assets impairment charge (Note G)			162
Purification Solutions goodwill impairment charge (Note G)			92
Income (loss) from operations	21	306	144
Interest and dividend income	8	9	10
Interest expense	(53)	(59)	(54)
Other income (expense)	(9)	(1)	17
Income (loss) from continuing operations before income taxes and equity in earnings of affiliated companies	(33)	255	117
(Provision) benefit for income taxes	(191)	(70)	(193)
Equity in earnings of affiliated companies, net of tax	3	1	2
Net income (loss)	(221)	186	(74)
Net income (loss) attributable to noncontrolling interests, net of tax of $4, $6 and $10	17	29	39
Net income (loss) attributable to Cabot Corporation	$ (238)	$ 157	$ (113)
Weighted-average common shares outstanding:
Basic	56.6	58.7	61.7
Diluted	56.6	58.8	61.7
Earnings per common share:
Basic	$ (4.21)	$ 2.64	$ (1.85)
Diluted	$ (4.21)	$ 2.63	$ (1.85)
Specialty Fluids [Member]
Loss on sale and asset impairment charge	$ 1	$ 29
Marshall Mine [Member]
Loss on sale and asset impairment charge	$ 129

Consolidated Statements of Op_2

Consolidated Statements of Operations (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Net income attributable to noncontrolling interests, tax amount	$ 4	$ 6	$ 10

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ (221)	$ 186	$ (74)
Other comprehensive income (loss), net of tax
Foreign currency translation adjustment, net of tax	42	(69)	(64)
Unrealized holding gains (losses) arising during the period, net of tax			(1)
Derivatives: net investment hedges
(Gains) losses reclassified to interest expense, net of tax	(5)	(4)	(3)
(Gains) losses excluded from effectiveness testing and amortized to interest expense, net of tax	2	1	1
Pension and other postretirement benefit liability adjustments, net of tax	9	(5)	5
Specialty Fluids divestiture		(3)
Other comprehensive income (loss)	48	(80)	(62)
Comprehensive income (loss)	(173)	106	(136)
Net income (loss) attributable to noncontrolling interests, net of tax	17	29	39
Foreign currency translation adjustment attributable to noncontrolling interests, net of tax	5	(6)	(4)
Comprehensive income (loss) attributable to noncontrolling interests	22	23	35
Comprehensive income (loss) attributable to Cabot Corporation	$ (195)	$ 83	$ (171)

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Sep. 30, 2020	Sep. 30, 2019
Current assets:
Cash and cash equivalents		$ 151	$ 169
Accounts and notes receivable, net of reserve for doubtful accounts of $2 and $3		418	530
Inventories		359	466
Prepaid expenses and other current assets		50	45
Total current assets		978	1,210
Property, plant and equipment		3,686	3,546
Accumulated depreciation		(2,372)	(2,198)
Net property, plant and equipment		1,314	1,348
Goodwill	[1]	134	90
Equity affiliates		39	39
Intangible assets, net		103	96
Deferred income taxes		53	163
Other assets		160	58
Total assets		2,781	3,004
Current liabilities:
Short-term borrowings		14	33
Accounts payable and accrued liabilities		488	537
Income taxes payable		20	22
Current portion of long-term debt		7	7
Total current liabilities		529	599
Long-term debt		1,094	1,024
Deferred income taxes		58	41
Other liabilities		286	206
Commitments and contingencies (Note U)
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: 56,616,030 and 57,250,454 shares, Outstanding: 56,466,638 and 57,080,589 shares		57	57
Less cost of 149,392 and 169,865 shares of common treasury stock		(4)	(5)
Retained earnings		989	1,337
Accumulated other comprehensive income (loss)		(351)	(391)
Total Cabot Corporation stockholders’ equity		691	998
Noncontrolling interests		123	136
Total stockholders’ equity		814	1,134
Total liabilities and stockholders’ equity		$ 2,781	$ 3,004
[1]

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Statement Of Financial Position [Abstract]
Accounts and notes receivable, reserve for doubtful accounts	$ 2	$ 3
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	56,616,030	57,250,454
Common stock, outstanding shares	56,466,638	57,080,589
Common treasury stock, shares	149,392	169,865

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Cash Flows from Operating Activities:
Net income (loss)	$ (221)	$ 186	$ (74)
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Depreciation and amortization	158	148	149
Impairment of investment in equity affiliate		11
Long-lived asset impairment charge			162
Goodwill impairment charge			92
Deferred tax provision (benefit)	130	(27)	91
Employee benefit plan settlement	4	7
Gain on sale of land			(39)
Gain on sale of investments			(10)
Equity in net income of affiliated companies	(3)	(1)	(2)
Non-cash compensation	9	11	22
Other non-cash (income) expense	8	(3)	16
Cash dividends received from equity affiliates	1	2	9
Changes in assets and liabilities:
Accounts and notes receivable	126	73	(127)
Inventories	114	27	(105)
Prepaid expenses and other current assets	(7)	18	(27)
Accounts payable and accrued liabilities	(55)	(75)	122
Income taxes payable	(5)	(6)	7
Other liabilities	(11)	(37)	12
Cash provided by operating activities	377	363	298
Cash Flows from Investing Activities:
Additions to property, plant and equipment	(200)	(224)	(229)
Proceeds from sale of business		135
Cash paid for acquisition of business, net of cash acquired of $1, $— and $1	(92)	(3)	(64)
Proceeds from the sale of land			39
Proceeds from sales of investments			11
Other	4	(2)	(3)
Cash used in investing activities	(288)	(94)	(246)
Cash Flows from Financing Activities:
Borrowings under financing arrangements		29
Repayments under financing arrangements		(29)	(4)
Increase (decrease) in short-term borrowings, net			(4)
Proceeds from (repayments of) issuance of commercial paper, net	(19)	(216)	249
Proceeds from long-term debt, net of issuance costs	444	352	90
Repayments of long-term debt	(410)	(75)	(251)
Repayments of redeemable preferred stock		(25)
Purchases of common stock	(44)	(173)	(142)
Proceeds from sales of common stock	3	4	22
Cash dividends paid to noncontrolling interests	(26)	(23)	(21)
Cash dividends paid to common stockholders	(80)	(80)	(80)
Cash used in financing activities	(132)	(236)	(141)
Effects of exchange rate changes on cash	25	(39)	(16)
Increase (decrease) in cash and cash equivalents	(18)	(6)	(105)
Cash and cash equivalents at beginning of year	169	175	280
Cash and cash equivalents at end of year	151	169	175
Non-cash investing activities and supplemental cash flow information:
Additions to property, plant and equipment included in Accounts payable and accrued liabilities	29	23	29
Income taxes paid	71	99	84
Interest paid	48	47	$ 47
Marshall Mine [Member]
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Loss on sale and asset impairment charge	$ 129
Specialty Fluids [Member]
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Loss on sale and asset impairment charge		$ 29

Consolidated Statements of Ca_2

Consolidated Statements of Cash Flows (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2018
Statement Of Cash Flows [Abstract]
Cash acquired in acquisition of business	$ 1	$ 1

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock, Net of Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total Cabot Corporation Stockholders' Equity [Member]	Noncontrolling Interests [Member]
Beginning Balance at Sep. 30, 2017	$ 1,625	$ 56		$ 1,707	$ (259)	$ 1,504	$ 121
Beginning Balance, Shares at Sep. 30, 2017		61,884
Net income (loss)	(74)			(113)		(113)	39
Total other comprehensive income (loss)	(62)				(58)	(58)	(4)
Acquisition of noncontrolling interest			$ (1)			(1)	1
Cash dividends declared to noncontrolling interests	(32)						(32)
Cash dividends paid to common stockholders, per share	(80)			(80)		(80)
Issuance of stock under equity compensation plans	22		22			22
Issuance of stock under equity compensation plans, Shares		733
Amortization of share-based compensation	22		22			22
Purchase and retirement of common stock	(142)	$ (2)	(43)	(97)		(142)
Purchase and retirement of common stock, Shares		(2,250)
Ending Balance at Sep. 30, 2018	1,279	$ 54		1,417	(317)	1,154	125
Ending Balance, Shares at Sep. 30, 2018		60,367
Net income (loss)	186			157		157	29
Total other comprehensive income (loss)	(80)				(74)	(74)	(6)
Acquisition of noncontrolling interest			(1)			(1)	1
Cash dividends declared to noncontrolling interests	(13)						(13)
Cash dividends paid to common stockholders, per share	(80)			(80)		(80)
Issuance of stock under equity compensation plans	4	$ 2	2			4
Issuance of stock under equity compensation plans, Shares		483
Amortization of share-based compensation	11		11			11
Purchase and retirement of common stock	(173)	$ (4)	(12)	(157)		(173)
Purchase and retirement of common stock, Shares		(3,769)
Ending Balance at Sep. 30, 2019	1,134	$ 52		1,337	(391)	998	136
Ending Balance, Shares at Sep. 30, 2019		57,081
Net income (loss)	(221)			(238)		(238)	17
Adoption of accounting standards				3	(3)
Total other comprehensive income (loss)	48				43	43	5
Cash dividends declared to noncontrolling interests	(35)						(35)
Cash dividends paid to common stockholders, per share	(80)			(80)		(80)
Issuance of stock under equity compensation plans	3	$ 2	1			3
Issuance of stock under equity compensation plans, Shares		330
Amortization of share-based compensation	9		9			9
Purchase and retirement of common stock	(44)	$ (1)	$ (10)	(33)		(44)
Purchase and retirement of common stock, Shares		(944)
Ending Balance at Sep. 30, 2020	$ 814	$ 53		$ 989	$ (351)	$ 691	$ 123
Ending Balance, Shares at Sep. 30, 2020		56,467

Consolidated Statements of Ch_2

Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - $ / shares	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Statement Of Stockholders Equity [Abstract]
Cash dividends paid, per share	$ 1.40	$ 1.36	$ 1.29

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Significant Accounting Policies	Note A. Significant Accounting Policies The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S. GAAP”). The significant accounting policies of Cabot Corporation (“Cabot” or “the Company”) are described below. Unless otherwise indicated, all disclosures and amounts in the Notes to the Consolidated Financial Statements relate to the Company’s continuing operations. Effective October 1, 2019, the Company adopted the accounting standard for leases issued by the Financial Accounting Standards Board (“FASB”) in February 2016. As discussed in Note C, effective April 1, 2020, the Company acquired Shenzhen Sanshun Nano New Materials Co., Ltd (“SUSN”), a leading carbon nanotube producer. The results of operations, and cash flows of SUSN are included in the Company’s consolidated financial statements from the date of acquisition. Principles of Consolidation The consolidated financial statements include the accounts of Cabot and its wholly-owned subsidiaries and majority-owned and controlled U.S. and non-U.S. subsidiaries. Additionally, Cabot considers consolidation of entities over which control is achieved through means other than voting rights, of which there were none in the periods presented. Intercompany transactions have been eliminated in consolidation. Cash and Cash Equivalents Cash equivalents include all highly liquid investments with a maturity of three months or less at date of acquisition. Cabot continually assesses the liquidity of cash equivalents and, as of September 30, 2020, has determined that they are readily convertible to cash. Inventories Inventories are stated at the lower of cost or net realizable value. The cost of inventories is determined using the first-in, first-out method. Cabot periodically reviews inventory for both potential obsolescence and potential declines in anticipated selling prices. In this review, the Company makes assumptions about the future demand for and market value of the inventory, and based on these assumptions estimates the amount of any obsolete, unmarketable, slow moving, or overvalued inventory. Cabot writes down the value of these inventories by an amount equal to the difference between the cost of the inventory and its estimated net realizable value. Investments The Company has investments in equity affiliates and marketable securities. As circumstances warrant, all investments are subject to periodic impairment reviews. Unless consolidation is required, investments in equity affiliates, where Cabot generally owns between 20% and 50% of the affiliate, are accounted for using the equity method. Cabot records its share of the equity affiliate’s results of operations based on its percentage of ownership of the affiliate. Dividends declared from equity affiliates are a return on investment and are recorded as a reduction to the equity investment value. In the second quarter of fiscal 2019, the Company recorded an impairment charge of $11 million related to its Venezuelan equity investment, which is included in Other income (expense) within the Consolidated Statements of Operations. Refer to Note M for details related to the impairment charge. At both September 30, 2020 and 2019, Cabot had equity affiliate investments of $39 million Intangible Assets and Goodwill Impairment The Company records tangible and intangible assets acquired and liabilities assumed in business combinations under the acquisition method of accounting. Amounts paid for an acquisition are allocated to the assets acquired and liabilities assumed based on their fair values at the date of acquisition. The Company uses assumptions and estimates in determining the fair value of assets acquired and liabilities assumed in a business combination. The determination of the fair value of intangible assets requires the use of significant judgment with regard to assumptions used in the valuation model. The Company estimates the fair value of identifiable acquisition-related intangible assets principally based on projections of cash flows that will arise from these assets. The projected cash flows are discounted to determine the fair value of the assets at the dates of acquisition. Definite-lived intangible assets, which are comprised of trademarks, customer relationships and developed technologies, are amortized over their estimated useful lives and are reviewed for impairment when indication of potential impairment exists, such as a significant reduction in cash flows associated with the assets. Goodwill is comprised of the purchase price of business acquisitions in excess of the fair value assigned to the net tangible and identifiable intangible assets acquired. Goodwill is not amortized and is subject to impairment testing annually, or when events or changes in the business environment indicate that the carrying value of the reporting unit may exceed its fair value. A reporting unit, for the purpose of the impairment test, is at or below the operating segment level, and constitutes a business for which discrete financial information is available and regularly reviewed by segment management. Reinforcement Materials, and the fumed metal oxides, specialty compounds, and specialty carbons product lines within Performance Chemicals, which are considered separate reporting units, carry the Company’s goodwill balances as of September 30, 2020. For the purpose of the goodwill impairment test, the Company first assesses qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If an initial qualitative assessment identifies that it is more likely than not that the carrying value of a reporting unit exceeds its estimated fair value, an additional quantitative evaluation is performed. Alternatively, the Company may elect to proceed directly to the quantitative goodwill impairment test. If based on the quantitative evaluation the fair value of the reporting unit is less than its carrying amount, a goodwill impairment loss would result. The goodwill impairment loss would be the amount by which the carrying value of the reporting unit, including goodwill, exceeds its fair value, limited to the total amount of goodwill allocated to that reporting unit. The fair value of a reporting unit is based on discounted estimated future cash flows. The fair value is also benchmarked against the value calculated from a market approach using the guideline public company method. The assumptions used to estimate fair value include management’s best estimates of future growth rates, operating cash flows, capital expenditures and discount rates over an estimate of the remaining operating period at the reporting unit level. Based on the Company’s most recent annual goodwill impairment test performed as of August 31, 2020, the fair values of the Reinforcement Materials, Fumed Metal Oxides, Specialty Compounds, and Specialty Carbons reporting units were substantially in excess of their carrying values. Long-lived Assets Impairment The Company’s long-lived assets primarily include property, plant and equipment, intangible assets, long-term investments and assets held for rent. The carrying values of long-lived assets are reviewed for impairment whenever events or changes in business circumstances indicate that the carrying amount of an asset may not be recoverable. To test for impairment of assets, the Company generally uses a probability-weighted estimate of the future undiscounted net cash flows of the assets over their remaining lives to determine if the value of the asset is recoverable. Long-lived assets are grouped with other assets and liabilities at the lowest level for which independent identifiable cash flows are determinable. An asset impairment is recognized when the carrying value of the asset is not recoverable based on the analysis described above, in which case the asset is written down to its fair value. If the asset does not have a readily determinable market value, a discounted cash flow model may be used to determine the fair value of the asset. In circumstances when an asset does not have separate identifiable cash flows, an impairment charge is recorded when the Company no longer intends to use the asset. Property, Plant and Equipment Property, plant and equipment are recorded at cost. Depreciation of property, plant and equipment is calculated using the straight-line method over the estimated useful lives of the related assets. The depreciable lives for buildings, machinery and equipment, and other fixed assets are generally between twenty and twenty-five years, ten and twenty-five years, and three and twenty-five years, respectively. The cost and accumulated depreciation for property, plant and equipment sold, retired, or otherwise disposed of are removed from the Consolidated Balance Sheets and resulting gains or losses are included in earnings in the Consolidated Statements of Operations. Expenditures for repairs and maintenance are charged to expenses as incurred. Expenditures for major renewals and betterments, which significantly extend the useful lives of existing plant and equipment, are capitalized and depreciated. Cabot capitalizes interest costs when they are part of the cost of acquiring and constructing certain assets that require a period of time to prepare for their intended use. During fiscal 2020, 2019 and 2018, Cabot capitalized $2 million, $4 million and $2 million of interest costs, respectively. These amounts are amortized over the lives of the related assets when they are placed in service. Asset Retirement Obligations Cabot estimates incremental costs for special handling, removal and disposal of materials that may or will give rise to conditional asset retirement obligations (“ARO”) and then discounts the expected costs back to the current year using a credit adjusted risk free rate. Cabot recognizes ARO liabilities and costs when the timing and/or settlement can be reasonably estimated. In certain instances, Cabot has not recorded a reserve for AROs because the timing of disposal of the underlying asset is unknown. The ARO reserves were $18 million and $26 million at September 30, 2020 and 2019, respectively, and are included in Accounts payable and accrued liabilities and Other liabilities on the Consolidated Balance Sheets. The decrease in the ARO reserve was due to the sale of Marshall Mine on September 30, 2020. Foreign Currency Translation The functional currency of the majority of Cabot’s foreign subsidiaries is the local currency in which the subsidiary operates. Assets and liabilities of foreign subsidiaries are translated into U.S. dollars at exchange rates in effect at the balance sheet dates. Income and expense items are translated at average monthly exchange rates during the year. Unrealized currency translation adjustments are included as a separate component of Accumulated other comprehensive income (loss) (“AOCI”) within stockholders’ equity. Realized and unrealized foreign currency gains and losses arising from transactions denominated in currencies other than the subsidiary’s functional currency are reflected in earnings with the exception of (i) intercompany transactions considered to be of a long-term investment nature; (ii) income taxes upon future repatriation of unremitted earnings from non-U.S. subsidiaries that are not indefinitely reinvested; and (iii) foreign currency borrowings designated as net investment hedges. Gains or losses arising from these transactions are included as a component of Other comprehensive income (loss). In fiscal 2020, 2019 and 2018, net foreign currency transaction loss of $6 million, Beginning July 1, 2018, the Argentina economy was determined to be highly inflationary. As a result, the functional currency of the Company’s Argentina subsidiary was changed to the U.S. dollar, Cabot’s reporting currency, which is discussed in Note M. Share Repurchases Periodically, Cabot repurchases shares of the Company’s common stock in the open market or in privately negotiated transactions under the authorization approved by the Board of Directors as discussed in Item 5 under the heading “Issuer Purchases of Equity Securities”. The Company retires the repurchased shares and records the excess of the purchase price over par value to additional paid-in capital (“APIC”) until such amount is reduced to zero and then charges the remainder against retained earnings. Financial Instruments Cabot’s financial instruments consist primarily of cash and cash equivalents, accounts and notes receivable, investments, accounts payable and accrued liabilities, short-term and long-term debt, and derivative instruments. The carrying values of Cabot’s financial instruments approximate fair value with the exception of fixed rate long-term debt, which is recorded at amortized cost. The fair values of the Company’s financial instruments are based on quoted market prices, if such prices are available. In situations where quoted market prices are not available, the Company relies on valuation models to derive fair value. Such valuation takes into account the ability of the financial counterparty to perform and the Company’s own credit risk. Cabot uses derivative financial instruments primarily for purposes of hedging the exposures to fluctuations in foreign currency exchange rates, which exist as part of its on-going business operations. Cabot does not enter into derivative contracts for speculative purposes, nor does it hold or issue any derivative contracts for trading purposes. All derivatives are recognized on the Consolidated Balance Sheets at fair value. Where Cabot has a legal right to offset derivative settlements under a master netting agreement with a counterparty, derivatives with that counterparty are presented on a net basis. The changes in the fair value of derivatives are recorded in either earnings or AOCI, depending on whether or not the instrument is designated as part of a hedge transaction and, if designated as part of a hedge transaction, the type of hedge transaction. The gains or losses on derivative instruments reported in AOCI are reclassified to earnings in the period in which earnings are affected by the underlying hedged item. The ineffective portion of all hedges is recognized in earnings during the period in which the ineffectiveness occurs. In accordance with Cabot’s risk management strategy, the Company may enter into certain derivative instruments that may not be designated as hedges for hedge accounting purposes. Although these derivatives are not designated as hedges, the Company believes that such instruments are closely correlated with the underlying exposure, thus managing the associated risk. The Company records in earnings the gains or losses from changes in the fair value of derivative instruments that are not designated as hedges. Cash movements associated with these instruments are presented in the Consolidated Statements of Cash Flows as Cash Flows from Operating Activities because the derivatives are designed to mitigate risk to the Company’s cash flow from operations. Revenue Recognition Cabot recognizes revenue when its customers obtain control of promised goods or services. The revenue recognized is the amount of consideration which the Company expects to receive in exchange for those goods or services. The Company’s contracts with customers are generally for products only and do not include other performance obligations. Generally, Cabot considers purchase orders, which in some cases are governed by master supply agreements, to be contracts with customers. The transaction price as specified on the purchase order or sales contract is considered the standalone selling price for each distinct product. To determine the transaction price at the time when revenue is recognized, the Company evaluates whether the price is subject to adjustments, such as for returns, discounts or volume rebates, which are stated in the customer contract, to determine the net consideration to which the Company expects to be entitled. Revenue from product sales is recognized based on a point in time model when control of the product is transferred to the customer, which typically occurs upon shipment or delivery of the product to the customer and title, risk and rewards of ownership have passed to the customer. The Company has an immaterial amount of revenue that is recognized over time. Payment terms typically range from zero to ninety days Shipping and handling activities that occur after the transfer of control to the customer are billed to customers and are recorded as sales revenue, as the Company considers these to be fulfillment costs. Shipping and handling costs are expensed in the period incurred and included in Cost of sales within the Consolidated Statement of Operations. Taxes collected on sales to customers are excluded from the transaction price. The Company generally provides a warranty that its products will substantially conform to the identified specifications. The Company’s liability typically is limited to either a credit equal to the purchase price or replacement of the non-conforming product. Returns under warranty have historically been immaterial. The Company does not have contract assets or liabilities that are material. As permitted by the revenue recognition standard, Revenue from Contracts with Customers Cost of Sales Cost of sales consists of the cost of raw and packaging materials, direct manufacturing costs, depreciation, internal transfer costs, inspection costs, inbound and outbound freight and shipping and handling costs, plant purchasing and receiving costs and other overhead expenses necessary to manufacture the products. Accounts and Notes Receivable Trade receivables are recorded at the invoiced amount and generally do not bear interest. Trade receivables in China may at certain times be settled with the receipt of bank issued non-interest bearing notes. These notes totaled 34 Cabot maintains allowances for doubtful accounts based on an assessment of the collectability of specific customer accounts, the aging of accounts receivable and other economic information on both a historical and prospective basis. Customer account balances are charged against the allowance when it is probable the receivable will not be recovered. There were no material changes in the allowance for any of the years presented. There is no material off-balance sheet credit exposure related to customer receivable balances. Stock-based Compensation Cabot recognizes compensation expense for stock-based awards granted to employees using the fair value method. Under the fair value recognition provisions, stock-based compensation cost is measured at the grant date based on the fair value of the award, and is recognized as expense over the service period, which generally represents the vesting period, and includes an estimate of what level of performance the Company will achieve for Cabot’s performance-based stock awards. Cabot calculates the fair value of its stock options using the Black-Scholes option pricing model. The fair value of restricted stock units is determined using the closing price of Cabot stock on the day of the grant. The Company recognizes forfeitures as they occur. Selling and Administrative Expenses Selling and administrative expenses consist of salaries and fringe benefits of sales and office personnel, general office expenses and other expenses not directly related to manufacturing operations. Research and Technical Expenses Research and technical expenses include salaries, equipment and material expenditures, and contractor fees and are expensed as incurred. Pensions and Other Postretirement Benefits The Company recognizes the funded status of defined benefit pension and other postretirement benefit plans as an asset or liability. This amount is defined as the difference between the fair value of plan assets and the benefit obligation. Pension and post-retirement benefit costs other than service cost are included in Other income (expense) in the Consolidated Statement of Operations. The Company is required to recognize as a component of Other comprehensive income (loss), net of tax, the actuarial gains/losses and prior service costs/credits that arise but were not previously required to be recognized as components of net periodic benefit cost. Other comprehensive income (loss) is adjusted as these amounts are later recognized in income as components of net periodic benefit cost. Accumulated Other Comprehensive Income (Loss) AOCI, which is included as a component of stockholders’ equity, includes unrealized gains or losses on derivative instruments, currency translation adjustments in foreign subsidiaries and minimum pension liability adjustments. Income Taxes Deferred income taxes are determined based on the estimated future tax effects of differences between financial statement carrying amounts and the tax bases of existing assets and liabilities. Deferred tax assets are recognized to the extent that realization of those assets is considered to be more likely than not. A valuation allowance is established for deferred taxes when it is more likely than not that all or a portion of the deferred tax assets will not be realized. Provisions are made for the U.S. income tax liability and additional non-U.S. taxes on the undistributed earnings of non-U.S. subsidiaries, except for amounts Cabot has designated to be indefinitely reinvested. Cabot records benefits for uncertain tax positions based on an assessment of whether the position is more likely than not to be sustained by the taxing authorities. If this threshold is not met, no tax benefit of the uncertain tax position is recognized. If the threshold is met, the tax benefit that is recognized is the largest amount that is greater than 50% likely of being realized upon ultimate settlement. This analysis presumes the taxing authorities’ full knowledge of the positions taken and all relevant facts, but does not consider the time value of money. The Company also accrues for interest and penalties on its uncertain tax positions and includes such charges in its income tax provision in the Consolidated Statements of Operations. Environmental Costs Cabot accrues environmental costs when it is probable that a liability has been incurred and the amount can be reasonably estimated. When a single liability amount cannot be reasonably estimated, but a range can be reasonably estimated, Cabot accrues the amount that reflects the best estimate within that range or the low end of the range if no estimate within the range is better. The amount accrued reflects Cabot’s assumptions about remediation requirements at the contaminated site, the nature of the remedy, the outcome of discussions with regulatory agencies and other potentially responsible parties at multi-party sites, and the number and financial viability of other potentially responsible parties. Cabot does not reduce its estimated liability for possible recoveries from insurance carriers. Proceeds from insurance carriers are recorded when realized by either the receipt of cash or a contractual agreement. Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make certain estimates and assumptions that affect the reported amount of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reported period. Actual results could differ from those estimates.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	12 Months Ended
	Sep. 30, 2020
Accounting Changes And Error Corrections [Abstract]
Recent Accounting Pronouncements	Note B. Recent Accounting Pronouncements Recently Adopted Accounting Standards In February 2016, the FASB issued a new standard for the accounting for leases. This standard requires lessees to recognize assets and liabilities for most leases, including operating leases that were previously not recorded on the balance sheet, and recognize expenses on their income statements in a manner that is similar to the historical accounting treatment for leases. The Company adopted the standard on October 1, 2019 using the modified retrospective optional transition method. Accordingly, leases in the prior period continue to be reported and disclosed in accordance with the Company’s historical accounting treatment. The Company elected the package of practical expedients that permits the Company to not reassess the identification, classification and initial direct costs of leases commencing before the October 1, 2019 effective date and to exclude short-term leases from the balance sheet. The Company did not elect the hindsight practical expedient to determine the lease term for existing leases or the practical expedient to not separate lease and non-lease components to existing leases, as well as new leases, through transition. The Company allocates the total consideration to the lease components and non-lease components on an observable stand-alone price basis to all asset classes. Adoption of the new lease standard resulted in the recognition of operating lease right-of-use (“ROU”) assets and operating lease liabilities of $106 million and $111 million, respectively, as of October 1, 2019. Refer to Note T for further details regarding the balance sheet classification of these items. The difference between the operating lease ROU assets and operating lease liabilities reflects the reclassification of historical deferred rent balances of $5 million. The effects of transition to the new standard resulted in no cumulative adjustment to retained earnings in the period of adoption. The standard did not materially impact the Company’s Consolidated Statement of Operations or Consolidated Statement of Cash Flows. The new standard did not have a material impact on the Company’s liquidity or debt-covenant compliance as of adoption. In February 2018, the FASB issued a new standard that allows entities to reclassify AOCI to Retained earnings stranded tax effects resulting from changes made as a result of the Tax Cuts and Jobs Act of 2017 (the “Act”). The Company adopted this standard on October 1, 2019 which resulted in the reclassification of a $2 million net gain from AOCI to Retained earnings. The reclassification was primarily related to the Company’s pension plans and derivative instruments. Recently Issued Accounting Pronouncements In June 2016, the FASB issued a new standard on measurement of credit losses. The standard introduces a new "expected loss" impairment model that applies to most financial assets measured at amortized cost and certain other instruments, including trade and other receivables and other financial assets. Entities are required to estimate expected credit losses over the life of financial assets and record an allowance against the assets’ amortized cost basis to present them at the amount expected to be collected. The new standard is effective for fiscal years beginning after December 15, 2019 and early adoption is permitted. The Company adopted this standard on October 1, 2020. The adoption of this standard did not materially impact the Company’s consolidated financial statements. 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.

Acquisitions

Acquisitions	12 Months Ended
	Sep. 30, 2020
Business Combinations [Abstract]
Acquisitions	Note C. Acquisitions NSCC Carbon (Jiangsu) Co. Ltd In September 2018 carbons and $2 and $4 million during fiscal 2020 and 2019, respectively. 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 a 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, and revenue totaled $12 million in the second half of fiscal 2020. The Company incurred acquisition and integration costs of $3 million through September 30, 2020 associated with the transaction, which are included in Selling and administrative expenses and Cost of sales in the Consolidated Statements of Operations. The final allocation of the purchase price set forth below was based on estimates of the fair value of assets acquired and liabilities assumed as of April 1, 2020. (In millions) Assets Cash $ 1 Accounts Receivable 8 Inventories 4 Prepaid expenses and other current assets 2 Property, plant and equipment 38 Intangible assets 15 Goodwill 45 Deferred tax asset 1 Other assets 2 Total assets acquired 116 Liabilities Accounts payable and accrued liabilities (12 ) Long-term debt (13 ) Other liabilities (6 ) Total liabilities assumed (31 ) Cash consideration paid $ 85 As part of the purchase price allocation, the Company determined the separately identifiable intangible assets are comprised of developed technologies of $9 million, which will be amortized over ten years, customer relationships of $4 million, which will be amortized over twenty years, and trademarks of $2 million, which will be amortized over ten years. The Company estimated the fair values of the identifiable acquisition-related intangible assets based on projections of cash flows that will arise from those assets. The projected cash flows were discounted to determine the fair value of the assets at the date of acquisition. The determination of the fair value of the intangible assets acquired required the use of judgment with regard to assumptions in the discounted cash flow model used and determination of the useful lives of the developed technologies, customer relationships and trademarks. The excess of the purchase price over the fair value of the tangible net assets and intangible assets acquired was recorded as goodwill. The goodwill recognized is attributable to the growth and operating synergies that the Company expects to realize from this acquisition. Goodwill generated from the acquisition will not be deductible for tax purposes.

Divestitures

Divestitures	12 Months Ended
	Sep. 30, 2020
Discontinued Operations And Disposal Groups [Abstract]
Divestitures	Note D. Divestitures Sale of Specialty Fluids Business In June 2019, the Company completed the sale of its Specialty Fluids business, an operating segment of the Company, to Sinomine for total proceeds of $133 million. he sale was subject to customary post-closing adjustments, which were finalized during the second quarter of fiscal 2020 and resulted in an additional pre-tax loss on sale of $1 million. Sale of Marshall Mine On September 30, 2020, the Company entered into an agreement to sell its lignite mine located in Marshall, Texas to ADA Carbon Solutions, LLC (“ADACS”) for a nominal amount. As part of the transaction, the Company agreed to fund a portion of the costs ADACS expects to incur to close the mine and included $9 million for these costs in Accounts payable and accrued liabilities and Other liabilities on the Consolidated Balance Sheets. The Company expects the majority of these costs to be paid within the next five years. At the sa In conjunction with the sale, the Company entered into a long-term supply agreement with ADACS, a producer of lignite-based activated carbon. ADACS will manufacture and supply the Purification Solutions business proprietary portfolio of lignite-based activated carbon products exclusively to the Company.

Inventories

Inventories	12 Months Ended
	Sep. 30, 2020
Inventory Disclosure [Abstract]
Inventories	Note E. Inventories Inventories, net of obsolete, unmarketable and slow moving reserves, are as follows: September 30 2020 2019 (In millions) Raw materials $ 82 $ 107 Finished goods 225 305 Other (1) 52 54 Total $ 359 $ 466 (1) Other inventory is comprised of certain spare parts and supplies. Cabot periodically reviews inventory for both obsolescence and loss of value. In this review, Cabot makes assumptions about the future demand for and market value of the inventory and, based on these assumptions, estimates the amount of obsolete, unmarketable or slow moving inventory. At September 30, 2020 and 2019, total inventory reserves were $ 28

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Property, Plant and Equipment	Note F. Property, Plant and Equipment Property, plant and equipment consists of the following: September 30 2020 2019 (In millions) Land and land improvements $ 111 $ 144 Buildings 552 524 Machinery and equipment 2,589 2,369 Other 244 247 Construction in progress 190 262 Total property, plant and equipment 3,686 3,546 Less: Accumulated depreciation (2,372 ) (2,198 ) Net property, plant and equipment $ 1,314 $ 1,348 Depreciation expense was $151 million for fiscal 2020 and $142 million for each of fiscal 2019 and 2018.

Purification Solutions Goodwill

Purification Solutions Goodwill and Long-Lived Assets Impairment Charges	12 Months Ended
	Sep. 30, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Purification Solutions Goodwill and Long-Lived Assets Impairment Charges	Note G. Purification Solutions Goodwill and Long-Lived Assets Impairment Charges During the second quarter of fiscal 2018, the Company performed a long-lived asset impairment test and quantitative goodwill impairment test, which determined that the estimated fair value of the Purification Solutions reporting unit was lower than the reporting unit's carrying value. The Company recorded impairment charges relating to the goodwill and long-lived assets of the Purification Solutions reporting unit, and an associated deferred tax benefit, in the Consolidated Statements of Operations as follows: Three Months Ended March 31, 2018 (In millions) Purification Solutions goodwill impairment charge $ 92 Purification Solutions long-lived assets impairment charge 162 Benefit for income taxes (30 ) Impairment charges, after tax $ 224 Prior to determining the goodwill impairment charge, the Company recorded an inventory reserve adjustment of $13 million in Cost of sales in the Consolidated Statements of Operations. Cabot will continue to monitor for events or changes in business circumstances that may indicate that the remaining carrying value of the asset group may not be recoverable.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Sep. 30, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Note H. Goodwill and Intangible Assets The carrying amount of goodwill attributable to each reportable segment with goodwill balances and the changes in those balances during the period ended September 30, 2020 are as follows: Reinforcement Materials Performance Chemicals Total (2) (In millions) Balance at September 30, 2019 $ 50 $ 40 90 Goodwill acquired (1) — 45 45 Foreign currency impact (4 ) 3 (1 ) Balance at September 30, 2020 $ 46 $ 88 $ 134 (1) (2) The following table provides information regarding the Company’s intangible assets: September 30, 2020 September 30, 2019 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 $ 60 $ (8 ) $ 52 $ 50 $ (5 ) $ 45 Trademarks 11 (1 ) 10 8 — 8 Customer relationships 56 (15 ) 41 57 (14 ) 43 Total intangible assets (1) $ 127 $ (24 ) $ 103 $ 115 $ (19 ) $ 96 (1) Total intangible assets as of September 30, 2020 includes $15 million of intangible assets from the acquisition of SUSN as described in Note C. Intangible assets are amortized over their estimated useful lives, which range between ten and twenty-five years, with a weighted average amortization period of 18 7

Accounts Payable, Accrued Liabi

Accounts Payable, Accrued Liabilities and Other Liabilities	12 Months Ended
	Sep. 30, 2020
Payables And Accruals [Abstract]
Accounts Payable, Accrued Liabilities and Other Liabilities	Note I. Accounts Payable, Accrued Liabilities and Other Liabilities Accounts payable and accrued liabilities included in current liabilities consist of the following: September 30 2020 2019 (In millions) Accounts payable $ 316 $ 390 Accrued employee compensation 46 51 Accrued legal expenses (1) 38 6 Other accrued liabilities 88 90 Total $ 488 $ 537 (1) Other long-term liabilities consist of the following: September 30 2020 2019 (In millions) Employee benefit plan liabilities $ 92 $ 91 Operating lease liabilities 89 — Non-current tax liabilities 9 12 Other accrued liabilities 96 103 Total $ 286 $ 206

Debt and Other Obligations

Debt and Other Obligations	12 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Debt and Other Obligations	Note J. Debt and Other Obligations Long-term Obligations The Company’s long-term obligations, the fiscal year in which they mature and their respective interest rates are summarized below: September 30 2020 2019 (In millions) Variable Rate Debt: Revolving Credit Facility, expires fiscal 2023 $ — $ — Revolving Credit Facility - Canada, expires fiscal 2021 — 43 Revolving Credit Facility - Euro, expires fiscal 2024 148 56 Total variable rate debt 148 99 Fixed Rate Debt: 3.7% Notes due fiscal 2022 350 350 3.4% Notes due fiscal 2026 250 250 4.0% Notes due fiscal 2029 300 300 Medium Term Notes: Notes due fiscal 2022, 8.34% — 8.47% 15 15 Notes due fiscal 2028, 6.57% — 7.28% 8 8 Total Medium Term Notes 23 23 Chinese Renminbi Debt, due fiscal 2020, 4.35% — 4 Chinese Renminbi Debt, due fiscal 2021, 4.35% 4 — Total fixed rate debt 927 927 Finance lease obligations (Note T) 31 12 Unamortized debt issuance costs and debt discount (5 ) (7 ) Total debt 1,101 1,031 Less current portion of long-term debt (7 ) (7 ) Total long-term debt $ 1,094 $ 1,024 Revolving Credit Facility, expiring fiscal 2023 — In October 2015, the Company entered into a revolving credit agreement with a loan commitment not to exceed $1 billion. The amount available for borrowing under the revolving credit agreement was $ 986 million as of September 30, 2020, and the weighted average interest rate on the outstanding balance during the year was 1.24%. The revolving credit agreement, which matures on October 23, 2022, supports the Company’s commercial paper program. Borrowings may be used for working capital, letters of credit and other general corporate purposes. The revolving credit agreement contains affirmative and negative covenants, a single financial covenant (consolidated total debt to consolidated earnings before interest, taxes, depreciation and amortization (“EBITDA”), as defined in the credit agreement) and events of default customary for financings of this type. Revolving Credit Facility-Canada expiring fiscal 2021 —In September 2018, a Canadian subsidiary entered into a revolving credit agreement with a loan commitment not to exceed 100 million U.S. dollars. The amount available for borrowing under this revolving credit agreement was $ 100 million as of September 30, 2020, and the weighted average interest rate on the outstanding balance during the year was 0.68%. The revolving credit agreement, which matures on September 24, 2021, subject to the right to request a one-year extension, may be used for working capital, capital expenditures and other general corporate purposes. The revolving credit agreement is guaranteed by Cabot Corporation. Revolving Credit Facility-Euro, expiring fiscal 2024 —In May 2019, several subsidiaries entered into a revolving credit agreement with a loan commitment not to exceed 300 million Euros. The amount available for borrowing under this revolving credit agreement was $ 204 million as of September 30, 2020, and the weighted average interest rate on the outstanding balance during the year was 1.90%. The revolving credit agreement, which matures on the earlier of (i) May 22, 2024 and (ii) the date of maturity, termination or expiration of the corporate revolving credit facility, may be used for repatriation of earnings of Cabot’s foreign subsidiaries to the U.S., the repayment of indebtedness of the Company’s foreign subsidiaries owing to the Company or any of its subsidiaries, and for working capital and general corporate purposes. The obligations of the subsidiaries under the revolving credit agreement are guaranteed by the Company. The Company paid debt issuance costs of $1 million upon entering the agreement, which are being amortized over the life of the revolver. Debt Covenants - As of September 30, 2020, the Company was in compliance with its debt covenants under the Credit Agreements, which, with limited exceptions, generally require the Company to comply on a quarterly basis with a leverage test requiring a ratio consolidated total debt to consolidated EBITDA for the four quarters then ending not to exceed 3.50 to 1.00. The Company amended the Credit Agreements as of June 8, 2020 to, among other things: (a) set the consolidated total debt to consolidated EBITDA ratio at 4.50 to 1.00 for the fiscal quarters ending September 30, 2020 through June 30, 2021, and (b) reduce the lien basket for other permitted liens securing Indebtedness (as defined in the Credit Agreements) in an aggregate amount at any time outstanding from 10% to 5% of Consolidated Tangible Net Worth (as defined in the Credit Agreements), at any time through and including June 30, 2021. Chinese Renminbi Debt —The Company’s consolidated Chinese subsidiaries had $4 million of unsecured long-term debt outstanding with a noncontrolling shareholder of a consolidated subsidiary as of both September 30, 2020 and 2019. 3.7% Notes due fiscal 2022 —In July 2012, Cabot issued $350 million in registered notes with a coupon of 3.7% that mature on July 15, 2022. These notes are unsecured and pay interest on January 15 and July 15. The net proceeds of this offering were $347 million after deducting discounts and issuance costs. The discount of less than $1 million was recorded at issuance and is being amortized over the life of the notes. 3.4% Notes due fiscal 2026 —In September 2016, Cabot issued $250 million in registered notes with a coupon of 3.4% that mature on September 15, 2026. These notes are unsecured and pay interest on March 15 and September 15. The net proceeds of this offering were $248 million after deducting discounts and issuance costs. The discount of less than $1 million was recorded at issuance and is being amortized over the life of the notes. 4.0% Notes due fiscal 2029 —In June 2019, Cabot issued $300 million in registered, unsecured, notes with a coupon of 4.0% that mature on July 1, 2029. Interest is payable under the notes semi-annually on January 1 and July 1 commencing in January 2020. The net proceeds of this offering were $296 million after deducting discounts and issuance costs of $1 million and $3 million, respectively, which were paid at issuance and are being amortized over the life of the notes. Medium Term Notes —At both September 30, 2020 and 2019, there were $ 23 million, of unsecured medium term notes outstanding issued to numerous lenders with various fixed interest rates and maturity dates. The weighted average maturity of the total outstanding medium term notes is 4 years 7.96 %. Finance Lease obligations —See Note T for a discussion of the Company’s leases. Future Years Payment Schedule The aggregate principal amounts of long-term debt, excluding finance lease liabilities presented separately in Note T, due in each of the five years from fiscal 2021 through 2025 and thereafter are as follows: Years Ending September 30 Principal Payments on Long-Term Debt (In millions) 2021 $ 4 2022 365 2023 — 2024 148 2025 — Thereafter 558 Total $ 1,075 Standby letters of credit —At September 30, 2020, the Company had provided standby letters of credit that were outstanding and not drawn totaling $ 6 million, which expire through fiscal 2022. Short-term Borrowings Commercial Paper —The Company has a commercial paper program and the maximum aggregate balance of commercial paper notes outstanding and the amounts borrowed under the revolving credit facility may not exceed the borrowing capacity of $1 billion under the revolving credit facility. The proceeds from the issuance of the commercial paper have been used for general corporate purposes, which may include working capital, refinancing existing indebtedness, capital expenditures, share repurchases, and acquisitions. The revolving credit facility is available to repay the outstanding commercial paper, if necessary . There was an outstanding balance of commercial paper of $ 14 0.28 Redeemable Preferred Stock In November 2013, the Company purchased all of its joint venture partner’s common stock in the former NHUMO, S.A. de C.V. (“NHUMO”) joint venture. At the close of the transaction, NHUMO issued redeemable preferred stock to the joint venture partner with a repurchase value of $25 million and a fixed dividend rate of 6% per annum. In November 2018, the Company repurchased the preferred stock for $25 million and paid a final dividend payment of $1.4 million.

Financial Instruments and Fair

Financial Instruments and Fair Value Measurements	12 Months Ended
	Sep. 30, 2020
Fair Value Disclosures [Abstract]
Financial Instruments and Fair Value Measurements	Note K. Financial Instruments and Fair Value Measurements The FASB authoritative guidance on fair value measurements defines fair value, provides a framework for measuring fair value, and requires certain disclosures about fair value measurements. The required disclosures focus on the inputs used to measure fair value. The guidance establishes the following hierarchy for categorizing these inputs: Level 1 — Quoted market prices in active markets for identical assets or liabilities Level 2 — Significant other observable inputs (e.g., quoted prices for similar items in active markets, quoted prices for identical or similar items in markets that are not active, inputs other than quoted prices that are observable such as interest rate and yield curves, and market-corroborated inputs) Level 3 — Significant unobservable inputs There were no transfers of financial assets or liabilities measured at fair value between Level 1 and Level 2, and there were no Level 3 investments during fiscal 2020 or 2019. At both September 30, 2020 and 2019, Cabot had derivatives relating to foreign currency risks carried at fair value. At September 30, 2020, the fair value of these derivatives was a net liability of $ 1 At September 30, 2020 and 2019, the fair value of Guaranteed investment contracts, included in Other assets on the Consolidated Balance Sheets, was $ 11 At both September 30, 2020 and 2019, 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 $ 1.08 1.18

Derivatives

Derivatives	12 Months Ended
	Sep. 30, 2020
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Derivatives	Note L. Derivatives Risk Management Cabot’s business operations are exposed to changes in interest rates, foreign currency exchange rates and commodity prices because Cabot finances certain operations through long and short-term borrowings, denominates transactions in a variety of foreign currencies and purchases certain commoditized raw materials. Changes in these rates and prices may have an impact on future cash flows and earnings. The Company manages these risks through normal operating and financing activities and, when deemed appropriate, through the use of derivative financial instruments. The Company has policies governing the use of derivative instruments and does not enter into financial instruments for trading or speculative purposes. By using derivative instruments, Cabot is subject to credit and market risk. If a counterparty fails to fulfill its performance obligations under a derivative contract, Cabot’s credit risk will equal the fair value of the derivative. Generally, when the fair value of a derivative contract is positive, the counterparty owes Cabot, thus creating a payment risk for Cabot. The Company minimizes counterparty credit (or repayment) risk by entering into transactions with major financial institutions of investment grade credit rating. Cabot’s exposure to market risk is not hedged in a manner that completely eliminates the effects of changing market conditions on earnings or cash flow. No significant concentration of credit risk existed at September 30, 2020 and 2019. Interest Rate Risk Management Cabot’s objective is to maintain a certain fixed-to-variable interest rate mix on the Company’s debt obligations. Cabot may enter into interest rate swaps as a hedge of the underlying debt instruments to effectively change the characteristics of the interest rate without changing the debt instrument. As of both September 30, 2020 and 2019, there were no derivatives held to manage interest rate risk. Foreign Currency Risk Management Cabot’s international operations are subject to certain risks, including currency exchange rate fluctuations and government actions. Cabot endeavors to match the currency in which debt is issued to the currency of the Company’s major, stable cash receipts. In some situations, Cabot has issued debt denominated in U.S. dollars and then entered into cross-currency swaps that exchange the dollar principal and interest payments into Euro denominated principal and interest payments. Additionally, the Company has foreign currency exposure arising from its net investments in foreign operations. Cabot may enter into cross-currency swaps to mitigate the impact of currency rate changes on the Company’s net investments. The Company also has foreign currency exposure arising from the denomination of monetary assets and liabilities in foreign currencies other than the functional currency of a given subsidiary as well as the risk that currency fluctuations could affect the dollar value of future cash flows generated in foreign currencies. Accordingly, Cabot uses short-term forward contracts to minimize the exposure to foreign currency risk. In certain situations where the Company has forecasted purchases under a long-term commitment or forecasted sales denominated in a foreign currency, Cabot may enter into appropriate financial instruments in accordance with the Company’s risk management policy to hedge future cash flow exposures. The following table provides details of the derivatives held as of September 30, 2020 and 2019 to manage foreign currency risk. Notional Amount Description Borrowing September 30, 2020 September 30, 2019 Hedge Designation Cross Currency Swaps 3.4% Notes USD 250 million swapped to EUR 223 million USD 250 million swapped to EUR 223 million Net investment Forward Foreign Currency Contracts (1) N/A USD 54 million USD 54 million No designation (1) As of September 30, 2020, Cabot’s forward foreign exchange contracts were denominated in Canadian dollar, Indonesian rupiah and Czech koruna. As of September 30, 2019, Cabot’s forward foreign exchange contracts were denominated in British pound, Canadian dollar, Indonesian rupiah and Czech koruna. Accounting for Derivative Instruments and Hedging Activities The Company determines the fair value of financial instruments using quoted market prices whenever available. When quoted market prices are not available for various types of financial instruments (such as forwards, options and swaps), the Company uses standard models with market-based inputs, which take into account the present value of estimated future cash flows and the ability of Cabot or the financial counterparty to perform. For interest rate and cross-currency swaps, the significant inputs to these models are interest rate curves for discounting future cash flows and are adjusted for credit risk. For forward foreign currency contracts, the significant inputs are interest rate curves for discounting future cash flows, and exchange rate curves of the foreign currency for translating future cash flows. Fair Value Hedge For derivative instruments that are designated and qualify as fair value hedges, the gain or loss on the derivative as well as the offsetting gain or loss on the hedged item attributable to the hedged risk are recognized in current period earnings. Cash Flow Hedge For derivative instruments that are designated and qualify as cash flow hedges, the effective portion of the gain or loss on the derivative is recorded in AOCI and reclassified to earnings in the same period or periods during which the hedged transaction affects earnings. Gains and losses on the derivative representing either hedge ineffectiveness or hedge components excluded from the assessment of effectiveness are recognized in current period earnings. Net Investment Hedge For net investment hedges, changes in the fair value of the effective portion of the derivatives’ gains or losses are reported as foreign currency translation gains or losses in AOCI while changes in the ineffective portion are reported in earnings. Effectiveness is assessed based on the hypothetical derivative method. The gains or losses on derivative instruments reported in AOCI are reclassified to earnings in the period in which earnings are affected by the underlying item, such as a disposal or substantial liquidations of the entities being hedged. The Company has cross-currency swaps with a notional amount of $250 million, which are designated as hedges of its net investments in certain Euro denominated subsidiaries. Cash settlements occur semi-annually on March 15 th th 4 1 2 1 5 The following table summarizes the impact of the cross-currency swaps to AOCI and the Consolidated Statements of Operations: Years Ended September 30 2020 2019 2018 2020 2019 2018 2020 2019 2018 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 $ 1 $ 23 $ (2 ) $ (5 ) $ (5 ) $ (5 ) $ 2 $ 1 $ 2 Other Derivative Instruments From time to time, the Company may enter into certain derivative instruments that may not be designated as hedges for accounting purposes, which may include cross-currency swaps, foreign currency forward contracts and commodity derivatives. For cross-currency swaps and foreign currency forward contracts not designated as hedges, the Company uses standard models with market-based inputs. The significant inputs to these models are interest rate curves for discounting future cash flows, and exchange rate curves of the foreign currency for translating future cash flows. In determining the fair value of the commodity derivatives, the significant inputs to valuation models are quoted market prices of similar instruments in active markets. Although these derivatives do not qualify for hedge accounting, Cabot believes that such instruments are closely correlated with the underlying exposure, thus managing the associated risk. The gains or losses from changes in the fair value of derivative instruments that are not accounted for as hedges are recognized in current period earnings. At both September 30, 2020 and 2019, the fair value of derivative instruments not designated as hedges were a nominal amount. At both September 30, 2020 and 2019, these instruments were presented in Prepaid expenses and other current assets on the Consolidated Balance Sheets.

Hyperinflationary Economies

Hyperinflationary Economies	12 Months Ended
	Sep. 30, 2020
Equity Method Investments And Joint Ventures [Abstract]
Hyperinflationary Economies	Note M. Hyperinflationary Economies Argentina Cabot owns 100% of a carbon black operating entity in Argentina. Beginning on July 1, 2018, the operating entity was considered to be functioning in a highly inflationary economy and began using Cabot’s reporting currency, the U.S. dollar, as its functional currency. There was no financial statement impact at the date of conversion due to the change in functional currency. Since the conversion, all impacts of foreign exchange changes between the reporting currency and Argentine peso are reflected in earnings in the Consolidated Statements of Operations. The Company’s income from operations was not significantly impacted from this change since the operating entity’s sales and a portion of its raw material purchases were already denominated in U.S. dollars. The operating entity’s net revenue represented 2 The operating entity’s assets and liabilities held in local currency, which consist primarily of cash and cash equivalents, inventories, property, plant and equipment and accounts payable and accrued liabilities, made up less than 2% of Cabot’s total assets and total liabilities at both September 30, 2020, and 2019. Changes in the Argentine peso exchange rate result in foreign currency exchange gains or losses on the operating entity’s peso-denominated monetary assets and liabilities. For fiscal 2020, 2019, and 2018, the Company recorded a net loss of $ 2 (income) expense in the Consolidated Statements of Operations, which reflects the remeasurement of the operating entity’s monetary assets and liabilities denominated in Argentine peso s using an exchange rate of , 57.32 , and 39.70 Argentine peso s to the U.S. dollar at September 30, 20 20 , 201 9 , and 2018, respectively . Venezuela Cabot owns 49% of a carbon black operating entity in Venezuela, which is accounted for as an equity affiliate, through wholly-owned subsidiaries that carry the investment and receive its dividends. While the operating entity had historically been profitable, it has not been operational in recent periods due to a lack of available raw materials. As such, in fiscal 2019, the Company performed an impairment analysis and determined that the decrease in fair value of the Venezuelan equity investment is other-than-temporary and that the investment is fully impaired. The Company recorded an impairment charge of $11 million in the second quarter of fiscal 2019, which is included in Other income (expense) within the Consolidated Statements of Operations. During the fourth quarter of fiscal 2020, the Venezuela entity was temporarily operational due to availability of raw materials.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Sep. 30, 2020
Compensation And Retirement Disclosure [Abstract]
Employee Benefit Plans	Note N. Employee Benefit Plans The information below provides detail concerning the Company’s benefit obligations under the defined benefit and postretirement benefit plans it sponsors. Defined benefit plans provide pre-determined benefits to employees that are distributed upon retirement. Cabot is making all sponsor required contributions to these plans. The accumulated benefit obligation was $99 million for the U.S. defined benefit plans and $ 215 The following provides information about projected benefit obligations, plan assets, the funded status and weighted-average assumptions of the defined benefit pension and postretirement benefit plans: Years Ended September 30 2020 2019 2020 2019 Pension Benefits Postretirement Benefits U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign (In millions) Change in Benefit Obligations: Benefit obligation at beginning of year $ 157 $ 220 $ 143 $ 373 $ 28 $ 20 $ 29 $ 19 Service cost 1 5 1 7 — — — — Interest cost 4 3 5 5 1 — 1 1 Plan participants’ contribution — 1 — 1 — — — — Foreign currency exchange rate changes — 7 — (13 ) — — — (1 ) Loss from changes in actuarial assumptions and plan experience 2 5 21 — 1 — 1 2 Benefits paid (7 ) (8 ) (11 ) (7 ) (3 ) — (3 ) (1 ) Settlements or curtailments (57 ) (2 ) (1 ) (134 ) — — — — Divestiture of Specialty Fluids — — — (13 ) — — — — Other (1 ) — (1 ) 1 — — — — Benefit obligation at end of year $ 99 $ 231 $ 157 $ 220 $ 27 $ 20 $ 28 $ 20 Years Ended September 30 2020 2019 2020 2019 Pension Benefits Postretirement Benefits U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign (In millions) Change in Plan Assets: Fair value of plan assets at beginning of year $ 151 $ 195 $ 149 $ 323 $ — $ — $ — $ — Actual return on plan assets 9 7 14 17 — — — — Employer contribution 1 6 1 7 3 — 3 1 Plan participants’ contribution — 1 — 1 — — — — Foreign currency exchange rate changes — 5 — (11 ) — — — — Benefits paid (7 ) (8 ) (11 ) (7 ) (3 ) — (3 ) (1 ) Settlements (57 ) (2 ) (1 ) (124 ) — — — — Divestiture — — — (10 ) — — — — Expenses paid from assets (1 ) — (1 ) (1 ) — — — — Fair value of plan assets at end of year $ 96 $ 204 $ 151 $ 195 $ — $ — $ — $ — Funded status $ (3 ) $ (27 ) $ (6 ) $ (25 ) $ (27 ) $ (20 ) $ (28 ) $ (20 ) Recognized asset (liability) $ (3 ) $ (27 ) $ (6 ) $ (25 ) $ (27 ) $ (20 ) $ (28 ) $ (20 ) Pension Assumptions and Strategy The following assumptions were used to determine the pension benefit obligations and periodic benefit costs as of and for the years ended September 30: 2020 2019 2018 Pension Benefits U.S. Foreign U.S. Foreign U.S. Foreign Actuarial assumptions as of the year-end measurement date: Discount rate 3.1 % 1.7 % 2.6 % 1.8 % 4.2 % 2.4 % Rate of increase in compensation N/A 3.0 % N/A 3.0 % N/A 2.7 % Cash balance interest credit rate 0.9 % 1.7 % 0.9 % 1.9 % 3.3 % 2.0 % Actuarial assumptions used to determine net periodic benefit cost during the year: Discount rate - benefit obligation 2.6 % 1.8 % 4.2 % 2.4 % 3.6 % 2.4 % Discount rate - service cost N/A 1.8 % N/A 2.5 % N/A 2.4 % Discount rate - interest cost 2.6 % 1.6 % 3.9 % 2.1 % 3.0 % 2.0 % Expected long-term rate of return on plan assets 2.5 % 5.2 % 6.3 % 4.9 % 6.8 % 4.9 % Rate of increase in compensation N/A 3.0 % N/A 2.7 % N/A 2.7 % Cash balance interest credit rate 0.9 % 1.9 % 3.3 % 2.0 % 3.3 % 2.0 % Postretirement Assumptions and Strategy The following assumptions were used to determine the postretirement benefit obligations and net costs as of and for the years ended September 30: 2020 2019 2018 Postretirement Benefits U.S. Foreign U.S. Foreign U.S. Foreign Actuarial assumptions as of the year-end measurement date: Discount rate 2.1 % 2.4 % 2.9 % 2.4 % 4.1 % 3.2 % Initial health care cost trend rate 6.0 % 6.9 % 6.5 % 6.9 % 7.0 % 7.0 % Actuarial assumptions used to determine net cost during the year: Discount rate - benefit obligation 2.9 % 2.4 % 4.1 % 3.2 % 3.4 % 3.1 % Discount rate - service cost 2.6 % 2.9 % 4.0 % 3.5 % 3.1 % 3.6 % Discount rate - interest cost 2.5 % 2.3 % 3.7 % 3.1 % 2.8 % 3.0 % Initial health care cost trend rate 6.5 % 6.9 % 7.0 % 7.0 % 7.0 % 7.1 % Cabot uses discount rates as of September 30, the plans’ measurement date, to determine future benefit obligations under its U.S. and foreign defined benefit plans. The discount rates for the defined benefit plans in Canada, the Eurozone, Japan, Switzerland, the United Arab Emirates, the United Kingdom and the U.S. are derived from yield curves that reflect high quality corporate bond yield or swap rate information in each region and reflect the characteristics of Cabot’s employee benefit plans. The discount rates for the defined benefit plans in Mexico, the Czech Republic and Indonesia are based on government bond indices that best reflect the durations of the plans, adjusted for credit spreads presented in selected AA corporate bond indices. The rates utilized are selected because they represent long-term, high quality, fixed income benchmarks that approximate the long-term nature of Cabot’s pension obligations and related payouts. Amounts recognized in the Consolidated Balance Sheets at September 30, 2020 and 2019 related to the Company's defined benefit pension and postretirement benefit plans were as follows: September 30 2020 2019 2020 2019 Pension Benefits Postretirement Benefits U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign (In millions) Other assets $ — $ 21 $ — $ 19 $ — $ — $ — $ — Accounts payable and accrued liabilities $ — $ (2 ) $ (3 ) $ (1 ) $ (3 ) $ (1 ) $ (3 ) $ — Other liabilities $ (3 ) $ (46 ) $ (3 ) $ (43 ) $ (24 ) $ (19 ) $ (25 ) $ (20 ) Amounts recognized in AOCI at September 30, 2020 and 2019 related to the Company's defined benefit pension and postretirement benefit plans were as follows: September 30 2020 2019 2020 2019 Pension Benefits Postretirement Benefits U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign (In millions) Net actuarial (gain) loss $ 6 $ 40 $ 13 $ 36 $ (4 ) $ 4 $ (6 ) $ 6 Net prior service credit — — — — — — — — Balance in accumulated other comprehensive income (loss), pretax $ 6 $ 40 $ 13 $ 36 $ (4 ) $ 4 $ (6 ) $ 6 Estimated Future Benefit Payments The Company expects that the following benefit payments will be made to plan participants in the years from 2021 to 2030: Pension Benefits Postretirement Benefits Years Ending September 30 U.S. Foreign U.S. Foreign (In millions) 2021 $ 96 $ 12 $ 3 $ 1 2022 $ — $ 10 $ 3 $ 1 2023 $ — $ 10 $ 3 $ 1 2024 $ — $ 12 $ 2 $ 1 2025 $ — $ 11 $ 2 $ 1 2026 - 2030 $ 1 $ 57 $ 9 $ 4 (1) Postretirement medical benefits are unfunded and impact Cabot’s cash flows as benefits become due, which is expected to be $4 million in fiscal 2021. The Company expects to contribute $ 5 Net periodic defined benefit pension and other postretirement benefit costs include the following components: Years Ended September 30 2020 2019 2018 2020 2019 2018 Pension Benefits Postretirement Benefits U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign (In millions) Service cost $ 1 $ 5 $ 1 $ 7 $ 1 $ 9 $ — $ — $ — $ — $ — $ — Interest cost 4 3 5 5 5 7 1 — 1 1 1 1 Expected return on plan assets (3 ) (9 ) (9 ) (10 ) (10 ) (15 ) — — — — — — Amortization of prior service cost — — — 2 — — — — (2 ) — (3 ) — Net losses — 3 — 2 — 3 (1 ) 1 (1 ) — (1 ) — Settlements or Curtailments cost 3 1 — (7 ) — — — — — — — — Net periodic (benefit) cost $ 5 $ 3 $ (3 ) $ (1 ) $ (4 ) $ 4 $ — $ 1 $ (2 ) $ 1 $ (3 ) $ 1 Other changes in plan assets and benefit obligations recognized in Other comprehensive income (loss) are as follows: Years Ended September 30 2020 2019 2018 2020 2019 2018 Pension Benefits Postretirement Benefits U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign (In millions) Net (gains) losses $ (4 ) $ 8 $ 14 $ (16 ) $ (4 ) $ — $ 1 $ (1 ) $ — $ 2 $ (2 ) $ (1 ) Prior service (credit) cost — — — 3 — — — — — — — — Amortization of prior service credit — — — (2 ) — — — — 2 — 3 — Amortization of prior unrecognized loss — (3 ) — (2 ) — (3 ) 1 (1 ) 1 — 1 — Loss on divestiture — — — (2 ) — — — — — — — — (Loss) gain on settlements (3 ) (1 ) — 7 — — — — — — — — Other — — — — — — — — — — — — Net changes recognized in Total other comprehensive (income) loss (1) $ (7 ) $ 4 $ 14 $ (12 ) $ (4 ) $ (3 ) $ 2 $ (2 ) $ 3 $ 2 $ 2 $ (1 ) (1) In fiscal 2019, the Company adjusted the assumptions in its U.K. plan to calculate accrued benefits for a portion of the plan’s participants. As a result of this change, a prior service cost of $2 million was recorded in Other income (expense) in the Consolidated Statements of Operations. Settlements of Employee Benefit Plans In fiscal 2019, the Company’s Board of Directors approved a resolution to terminate the U.S. pension plan. The Company commenced the U.S. plan termination process during the third quarter of 2019 and completed the transfer of the U.S. plan’s assets in the first quarter of fiscal 2021. The pension liability was settled through a combination of lump-sum payments and purchased annuities, neither of which required an additional cash contribution. In the fourth quarter of fiscal 2020, the Company recognized a settlement loss 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 2021, the company will recognize an additional $6 million settlement loss In fiscal 2019, the Company transferred the majority of the defined benefit obligations and pension plan assets in one of its foreign defined benefit plans to a multi-employer plan. This action moved the administrative, asset custodial, asset investment, actuarial, communication and benefit payment obligations to the multi-employer fund administrator. As a result of the transfer, In fiscal 2020 and 2019, Cabot’s pension benefit obligations decreased by $47 million and $139 million, respectively, which was driven in fiscal 2020 by the U.S. pension plan termination and in fiscal 2019 by the transfer of the foreign defined benefit plan to a multi-employer plan discussed above. Plan Assets The Company’s defined benefit pension plans weighted-average asset allocations at September 30, 2020 and 2019 by asset category, are as follows: September 30 2020 2019 Pension Assets U.S. Foreign U.S. Foreign Equity securities — % 39 % — % 39 % Debt securities 95 % 50 % 68 % 50 % Real estate — % 6 % — % 6 % Cash and other securities 5 % 5 % 32 % 5 % Total 100 % 100 % 100 % 100 % To develop the expected long-term rate of return on plan assets assumption, the Company used a capital asset pricing model. The model considers the current level of expected returns on risk-free investments comprised of government bonds, the historical level of the risk premium associated with the other asset classes in which the portfolio is invested, and the expectations for future returns for each asset class. The expected return for each asset class was then weighted based on the target asset allocation to develop the expected long-term rate of return for each plan. Cabot’s investment strategy for each of its foreign defined benefit plans is generally based on a set of investment objectives and policies that cover time horizons and risk tolerance levels consistent with plan liabilities. Periodic studies are performed to determine the asset mix that will meet pension obligations at a reasonable cost to the Company. The assets of the defined benefit plans are comprised principally of investments in equity and high-quality fixed income securities, which are broadly diversified across the capitalization and style spectrum and are managed using both active and passive strategies. The weighted average target asset allocation for the foreign plans is 41% in equity, 49% in fixed income, 6% in real estate, and 4% in cash and other securities. The asset allocation of the U.S. Pension was targeted as a result of the plan settlement discussed in the Settlements of Employee Benefit Plans section above and the assets were fully transferred in the first quarter of fiscal 2021. For pension plan assets classified as Level 1 measurements (measured using quoted prices in active markets), total fair value is either the price of the most recent trade at the time of the market close or the official close price, as defined by the exchange on which the asset is most actively traded on the last trading day of the period, multiplied by the number of units held without consideration of transaction costs. For pension plan assets classified as Level 2 measurements, where the security is frequently traded in less active markets, fair value is based on the closing price at the end of the period; where the security is less frequently traded, fair value is based on the price a dealer would pay for the security or similar securities, adjusted for any terms specific to that asset or liability. Market inputs are obtained from well-established and recognized vendors of market data and subjected to tolerance/quality checks. The fair value of the Company’s pension plan assets at September 30, 2020 and 2019 by asset category is as follows: September 30 2020 2019 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Total (In millions) Cash $ 4 $ — $ 4 $ 2 $ — $ 2 Direct investments: U.S government bonds 12 — 12 — — — U.S. corporate bonds 84 — 84 — — — Non-U.S. equities 4 — 4 3 — 3 Non-U.S. government bonds 2 — 2 2 — 2 Non-U.S. corporate bonds 3 — 3 3 — 3 Mortgage backed securities — 1 1 — 1 1 Other fixed income 1 — 1 1 — 1 Total direct investments 106 1 107 9 1 10 Investment funds: Equity funds (1) — 76 76 — 74 74 Fixed income funds (2) — 95 95 104 90 194 Real estate funds (3) — 12 12 — 12 12 Cash equivalent funds 1 — 1 48 — 48 Total investment funds 1 183 184 152 176 328 Alternative investments: Insurance contracts (4) — 5 5 — 5 5 Other alternative investments — — — 1 — 1 Total alternative investments — 5 5 1 5 6 Total pension plan assets $ 111 $ 189 $ 300 $ 164 $ 182 $ 346 (1) The equity funds asset class includes funds that invest in U.S. equities as well as equity securities issued by companies incorporated, listed or domiciled in countries in developed and/or emerging markets. These companies may be in the small-, mid- or large-cap categories. (2) The fixed income funds asset class includes investments in high quality funds. High quality fixed income funds primarily invest in low risk U.S. and non-U.S. government securities, investment-grade corporate bonds, mortgages and asset-backed securities. A significant portion of the fixed income funds include investment in long-term bond funds. (3) The real estate funds asset class includes funds that primarily invest in entities which are principally engaged in the ownership, acquisition, development, financing, sale and/or management of income-producing real estate properties, both commercial and residential. These funds typically seek long-term growth of capital and current income that is above average relative to public equity funds. (4) Insurance contracts held by the Company’s non-U.S. plans are issued by well-known, highly rated insurance companies. Defined Contribution Plans In addition to benefits provided under the defined benefit and postretirement benefit plans, the Company provides benefits under defined contribution plans. Cabot recognized expenses related to these plans of $19 million in fiscal 2020, $20 million in fiscal 2019, and $19 million in fiscal 2018.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation	Note O. Stock-Based Compensation The Cabot Corporation 2017 Long-Term Incentive Plan (the “2017 Plan”) was established by the Company to provide stock-based compensation to eligible employees. The 2017 Plan was approved by Cabot’s stockholders on March 9, 2017 and authorizes the issuance of up to 5,375,000 shares of common stock. It is the only equity incentive plan under which the Company may grant equity awards to employees. The terms of awards made under Cabot’s equity compensation plans are generally determined by the Compensation Committee of Cabot’s Board of Directors. The awards made in fiscal 2020, 2019 and 2018 consist of grants of stock options, time-based restricted stock units, and performance-based restricted stock units. The options were issued with an exercise price equal to 100% of the market price of Cabot’s common stock on the date of grant, generally vest over a three year period (30% on each of the first and second anniversaries of the date of grant and 40% on the third anniversary of the date of grant) and have a ten-year three-year Stock-based employee compensation expense was $ 9 The Company recognized the full impact of its stock-based employee compensation expense in the Consolidated Statements of Operations for fiscal 2020, 2019 and 2018 and did not capitalize any such costs on the Consolidated Balance Sheets because those that qualified for capitalization were not material. The following table presents stock-based compensation expenses included in the Company’s Consolidated Statements of Operations: Years Ended September 30 2020 2019 2018 (In millions) Cost of sales $ 1 $ 1 $ 2 Selling and administrative expenses 7 9 19 Research and technical expenses 1 1 1 Stock-based compensation expense 9 11 22 Income tax benefit — (3 ) (6 ) Net stock-based compensation expense $ 9 $ 8 $ 16 As of September 30, 2020, Cabot had $ 10 approximately one year Equity Incentive Plan Activity The following table summarizes the total stock option and restricted stock unit activity in the equity incentive plans for fiscal 2020: Stock Options Restricted Stock Units Total Options (4) Weighted Average Exercise Price Weighted Average Grant Date Fair Value Restricted Stock Units (1) Weighted Average Grant Date Fair Value (Shares in thousands) Outstanding at September 30, 2019 1,022 $ 50.57 $ 12.13 765 $ 53.71 Granted 333 $ 50.23 $ 10.68 276 $ 49.36 Performance-based adjustment (2) — $ — $ — (102 ) $ 53.02 Exercised / Vested (29 ) $ 46.76 $ 6.07 (261 ) $ 50.67 Cancelled / Forfeited (53 ) $ 53.60 $ 7.07 (74 ) $ 55.74 Outstanding at September 30, 2020 (3) 1,273 $ 50.45 $ 11.74 604 $ 52.87 Exercisable at September 30, 2020 664 $ 49.59 (1) The number granted represents the number of shares issuable upon vesting of time-based restricted stock units and performance-based restricted stock units, assuming the Company performs at the target performance level in each year of the three-year performance period. (2) Represents the net incremental number of shares cancelled based on the Company’s actual financial performance metrics for fiscal 20 20 . (3) Stock options outstanding include options vested and expected to vest in the future and have a weighted average remaining contractual life of 6.66 (4) Unvested stock options were approximately 609,000 51.38 Stock Options As of September 30, 2020, the aggregate intrinsic value for all options outstanding and options exercisable was nil since the Company’s closing stock price of $36.03 at September 30, 2020 was below their weighted average exercise price. The intrinsic value of options exercised during fiscal 2020, 2019 and 2018 was nominal 1 The Company uses the Black-Scholes option-pricing model to estimate the fair value of the options at the grant date. The weighted average grant date fair values of options granted during fiscal 2020, 2019 and 2018 was $ 10.68 Years Ended September 30 2020 2019 2018 Expected stock price volatility 28 % 27 % 28 % Risk free interest rate 1.9 % 3.1 % 2.2 % Expected life of options (years) 6 6 6 Expected annual dividends per year $ 1.40 $ 1.32 $ 1.26 The expected stock price volatility assumption was determined using the historical volatility of the Company’s common stock over the expected life of the option. The expected term reflects the anticipated time period between the measurement date and the exercise date or post-vesting cancellation date. Restricted Stock Units The value of restricted stock unit awards is the closing stock price at the date of the grant. The weighted average grant date fair values of restricted stock unit awards granted during fiscal 2020, 2019 and 2018 was $ 49.36 13 Supplemental 401(k) Plan Cabot’s Deferred Compensation and Supplemental Retirement Plan (“SERP 401(k)”) provides benefits to highly compensated employees when the retirement plan limits established under the Internal Revenue Code prevent them from receiving all of the Company matching and retirement contributions that would otherwise be provided under the qualified 401(k) plan. The SERP 401(k) is non-qualified and unfunded. Contributions under the SERP 401(k) are treated as if invested in Cabot common stock. The majority of the distributions made under the SERP 401(k) are required to be paid with shares of Cabot common stock. The remaining distributions, which relate to certain grandfathered accounts, will be paid in cash based on the market price of Cabot common stock at the time of distribution. The aggregate value of the accounts that will be paid out in stock, which is equivalent to approximately 76,000

Restructuring

Restructuring	12 Months Ended
	Sep. 30, 2020
Restructuring And Related Activities [Abstract]
Restructuring	Note P. Restructuring Cabot’s restructuring activities were recorded in the Consolidated Statements of Operations as follows: Years Ended September 30 2020 2019 2018 (In millions) Cost of sales $ 6 $ 9 $ (31 ) Selling and administrative expenses 13 7 1 Total $ 19 $ 16 $ (30 ) Details of all restructuring activities and the related reserves for fiscal 2018, 2019, and 2020 were as follows: Severance and Employee Benefits Environmental Remediation and Decommissioning Activities Non-Cash Asset Impairment and Accelerated Depreciation Asset Sales Other Total (In millions) Reserve at September 30, 2017 $ 1 $ 2 $ — $ — $ — $ 3 Charges (gain) 2 3 1 (38 ) 2 (30 ) Costs charged against assets — — (1 ) (1 ) — (2 ) Cash (paid) received (2 ) (1 ) — 39 (2 ) 34 Reserve at September 30, 2018 1 4 — — — 5 Charges (gain) 11 — 2 — 3 16 Costs charged against liabilities — — (2 ) — — (2 ) Cash paid (9 ) — — — (3 ) (12 ) Reserve at September 30, 2019 3 4 — — — 7 Charges (gain) 14 — 1 — 4 19 Costs charged against assets — — (1 ) — — (1 ) Cash (paid) received (12 ) — — — (4 ) (16 ) Reserve at September 30, 2020 $ 5 $ 4 $ — $ — $ — $ 9 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 fiscal 2020, the Company recorded charges of $17 million for these actions, primarily related to severance costs. The Company expects to record additional restructuring charges, primarily related to site demolition and clearing costs associated with the Company’s other operational efficiency initiatives, of approximately $1 million in fiscal 2021 and $3 million thereafter. Cabot paid $13 million related to these activities in fiscal 2020 and expects to pay $4 million in fiscal 2021 and $4 million thereafter. As of September 30, 2020, Cabot had $4 million of accrued severance charges in the Consolidated Balance Sheets related to these actions. Purification Solutions Transformation Plan In fiscal 2018, the Company began implementation of a transformation plan to improve the long-term performance of the Purification Solutions segment. The purpose of the plan is to focus the business’s product portfolio, optimize its manufacturing assets, and streamline its organizational structure to support the new focus. As part of this plan, the Company idled the activation kilns at its manufacturing facility in Marshall, Texas in September 2020, which is discussed in Note D. The Company recorded charges of $2 million related to the transformation plan in fiscal 2020, primarily related to severance costs. Cabot recorded charges of $ 9 8 1 1 8 2 1 Sale of Land Rights in Thane, India During fiscal 2018, Cabot entered into a binding memorandum of understanding to sell its land rights in Thane, India for $28 million. Based on the execution of the binding agreement and non-refundable receipt of cash for the full amount, the Company has recorded the pre-tax gain on sale of $28 million to Cost of sales in the Consolidated Statements of Operations in fiscal 2018. 2016 Plan As part the Company’s 2016 restructuring plan, the Company ceased operations at its carbon black manufacturing facility in Merak, Indonesia in January 2016 and completed the sale of the land on which the facility was located in fiscal 2018 for cash consideration totaling $13 million, resulting in a net pre-tax gain of $11 million recorded to Cost of sales in the Company’s Consolidated Statements of Operations.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Sep. 30, 2020
Stockholders Equity Note [Abstract]
Accumulated Other Comprehensive Income (Loss)	Note Q. Accumulated Other Comprehensive Income (Loss) Changes in each component of AOCI, net of tax, are as follows for fiscal 2019 and 2020: Currency Translation Adjustment Unrealized Gains on Investment Pension and Other Postretirement Benefit Liability Adjustment Total (In millions) Balance at September 30, 2018 attributable to Cabot Corporation $ (266 ) $ 1 $ (52 ) $ (317 ) Other comprehensive income (loss) before reclassifications (69 ) — 4 (65 ) Amounts reclassified from AOCI (9 ) — (6 ) (15 ) Less: Other comprehensive income (loss) attributable to noncontrolling interests (6 ) — — (6 ) Balance at September 30, 2019 attributable to Cabot Corporation (338 ) 1 (54 ) (391 ) Other comprehensive income (loss) before reclassifications 42 — 3 45 Amounts reclassified from AOCI (3 ) — 6 3 Adoption of accounting standards (3 ) (1 ) 1 (3 ) Less: Other comprehensive income (loss) attributable to noncontrolling interests 5 — — 5 Balance at September 30, 2020 attributable to Cabot Corporation $ (307 ) $ — $ (44 ) $ (351 ) The amounts reclassified out of AOCI and into the Consolidated Statements of Operations for fiscal 2020, 2019 and 2018 are as follows: Affected Line Item in the Consolidated Years Ended September 30 Statements of Operations 2020 2019 2018 (In Millions) Derivatives: net investment hedges (Gains) losses reclassified to interest expense Interest expense $ (5 ) $ (5 ) $ (5 ) (Gains) losses excluded from effectiveness testing and amortized to interest expense Interest expense 2 1 2 Pension and other postretirement benefit liability adjustment Amortization of actuarial losses and prior service cost (credit) Net Periodic Benefit Cost - see Note N for details 3 1 (1 ) Settlement and curtailment loss (gain) Net Periodic Benefit Cost - see Note N for details 4 (7 ) — Specialty Fluids divestiture Specialty Fluids loss on sale and asset impairment - see Note D for details — (3 ) — Total before tax 4 (13 ) (4 ) Tax impact Provision (benefit) for income taxes (1 ) (2 ) 1 Total after tax $ 3 $ (15 ) $ (3 )

Earnings Per Share

Earnings Per Share	12 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Earnings Per Share	Note R. Earnings Per Share The following tables summarize the components of the basic and diluted earnings per common share (“EPS”) computations: Years Ended September 30 2020 2019 2018 (In millions, except per share amounts) Basic EPS: Net income (loss) attributable to Cabot Corporation $ (238 ) $ 157 $ (113 ) Less: Dividends and dividend equivalents to participating securities — 1 1 Less: Undistributed earnings allocated to participating securities (1) — 1 — Earnings (loss) allocated to common shareholders (numerator) $ (238 ) $ 155 $ (114 ) Weighted average common shares and participating securities outstanding 57.3 59.5 62.4 Less: Participating securities (1) 0.7 0.8 0.7 Adjusted weighted average common shares (denominator) 56.6 58.7 61.7 Per share amounts—basic: Net income (loss) attributable to Cabot Corporation $ (4.21 ) $ 2.64 $ (1.85 ) Diluted EPS: Earnings (loss) allocated to common shareholders $ (238 ) $ 155 $ (114 ) Plus: Earnings allocated to participating securities — 2 — Less: Adjusted earnings allocated to participating securities (2) — 2 — Earnings (loss) available to common shares (numerator) $ (238 ) $ 155 $ (114 ) Adjusted weighted average common shares outstanding 56.6 58.7 61.7 Effect of dilutive securities: Common shares issuable (3) — 0.1 — Adjusted weighted average common shares (denominator) 56.6 58.8 61.7 Per share amounts—diluted: Net income (loss) attributable to Cabot Corporation $ (4.21 ) $ 2.63 $ (1.85 ) (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: Years Ended September 30 2020 2019 2018 (In millions) Calculation of undistributed earnings: Net income (loss) attributable to Cabot Corporation $ (238 ) $ 157 $ (113 ) Less: Dividends declared on common stock 80 80 79 Less: Dividends and dividend equivalents to participating securities — 1 1 Undistributed earnings (loss) $ (318 ) $ 76 $ (193 ) Allocation of undistributed earnings: Undistributed earnings (loss) allocated to common shareholders $ (318 ) $ 75 $ (193 ) Undistributed earnings allocated to participating securities — 1 — Undistributed earnings (loss) $ (318 ) $ 76 $ (193 ) (2) (3)

Income Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Note S. Income Taxes Income from continuing operations before income taxes and equity in net earnings of affiliated companies was as follows: Years Ended September 30 2020 2019 2018 (In millions) Domestic $ (274 ) $ (66 ) $ (229 ) Foreign 241 321 346 Income from continuing operations before income taxes and equity in earnings of affiliated companies $ (33 ) $ 255 $ 117 Tax provision (benefit) for income taxes consisted of the following: Years Ended September 30 2020 2019 2018 (In millions) U.S. federal and state: Current $ (1 ) $ 2 $ 14 Deferred 139 (30 ) 114 Total 138 (28 ) 128 Foreign: Current 62 95 88 Deferred (9 ) 3 (23 ) Total 53 98 65 Provision (benefit) for income taxes $ 191 $ 70 $ 193 The provision ( benefit Years Ended September 30 2020 2019 2018 (In millions) Computed tax expense at the federal statutory rate $ (7 ) $ 53 $ 29 Foreign impact of taxation at different rates, repatriation, valuation allowance, and other 4 17 (8 ) Impact of the Tax Cuts and Jobs Act of 2017 — — 159 Global Intangible Low Taxed Income (GILTI) (4 ) 10 — Impact of the Coronavirus Aid, Relief, and Economic Security ("CARES") Act of 2020 (10 ) — — Impact of increase (decrease) in valuation allowance on U.S. deferred taxes 228 — — U.S. and state benefits from research and experimentation activities (2 ) (2 ) (2 ) Provision (settlement) of unrecognized tax benefits (7 ) (8 ) 1 Impact of goodwill impairment charge — — 18 Permanent differences, net — 1 (1 ) State taxes, net of federal effect (11 ) (1 ) (3 ) Provision (benefit) for income taxes $ 191 $ 70 $ 193 In July 2020, final U.S. tax regulations were issued regarding the Global Intangible Low Taxed Income High-Tax exception (“GILTI” ”HTE"), allowing taxpayers to exclude from GILTI income of a Controlled Foreign Corporation (“CFC”) that incurs a foreign tax rate more than 90% of the top U.S. corporate tax rate. A GILTI HTE election may be made on an annual basis, and taxpayers may choose to apply the election to taxable years beginning after December 31, 2017. Cabot expects to make the GILTI HTE election for fiscal 2020 and 2019 and therefore recorded the impact of making the election for fiscal 2020 as well as a retrospective election for fiscal 2019 in full during the fourth quarter of fiscal 2020. Significant components of deferred income taxes were as follows: September 30 2020 2019 (In millions) Deferred tax assets: Deferred expenses $ 19 $ 15 Intangible assets 37 28 Inventory 13 9 Operating lease liability 20 — Other 32 3 Pension and other benefits 35 41 Net operating loss carryforwards 109 124 Foreign tax credit carryforwards 58 20 R&D credit carryforwards 44 43 Other business credit carryforwards 23 29 Subtotal 390 312 Valuation allowance (317 ) (124 ) Total deferred tax assets $ 73 $ 188 September 30 2020 2019 (In millions) Deferred tax liabilities: Property, plant and equipment $ (40 ) $ (61 ) Right of use asset (20 ) - Unremitted earnings of non-U.S. subsidiaries (18 ) (5 ) Total deferred tax liabilities $ (78 ) $ (66 ) The Company assesses the available positive and negative evidence to estimate whether sufficient future taxable income will be generated to permit utilization of the existing deferred tax assets. When performing this assessment, the Company looks to the potential future reversal of existing taxable temporary differences, taxable income in carryback years and the feasibility of tax planning strategies and estimated future taxable income. Failure to achieve operating income targets resulting in a cumulative loss may change the Company’s assessment regarding the realization of Cabot’s deferred tax assets, resulting in valuation allowance being recorded against some or all of the Company’s deferred tax assets. The need for a valuation allowance can also be affected by changes to tax laws, changes to statutory tax rates and changes to future taxable income estimates. A valuation allowance represents management’s best estimate of the non-realizable portion of the deferred tax assets. Any adjustments in a valuation allowance would result in an adjustment to income tax expense. In determining the recoverability of its U.S. deferred tax assets, the Company considered its cumulative loss incurred over the three-year period ended September 30, 2020. Such objective negative evidence limits the Company’s ability to consider other subjective evidence, such as its projections for future growth. Given the weight of objectively verifiable historical losses from the Company's U.S. operations, the Company has recorded a valuation allowance on all of its U.S. deferred tax assets of $253 million comprised of $18 million of U.S. state net operating loss carryforwards (“NOLs”), $58 million of foreign tax credits, $44 million of U.S. R&D credits, $19 million of state tax credits and $114 million of other net deferred tax assets (primarily composed of deferred expenses) during the fourth quarter of fiscal 2020. The Company expects to continue to record a valuation allowance against these assets until sufficient positive evidence exists to support its reversal. The valuation allowance increased by $193 million in fiscal 2020 compared to fiscal 2019 primarily due to the recording of a valuation allowance charge against all of the Company’s U.S. net deferred tax assets of $228 million as of September 30, 2020, of which $132 million existed at the beginning of the year and $96 million was generated during fiscal 2020 resulting in a $253 million valuation allowance against all U.S. net deferred tax assets. The foreign valuation allowance decreased $32 million primarily due to the expiration of net operation losses against which a valuation allowance was recorded. The valuation allowance decreased by $45 million in fiscal 2019 primarily due to the release of valuation allowance from the expiration of net operating losses in certain jurisdictions and the divestiture of the Company’s Specialty Fluids business of $16 million. After the valuation allowance, approximately $32 million of foreign NOLs and less than $1 million of other tax credit carryforwards remained at September 30, 2020. The benefits of these carryforwards are dependent upon taxable income during the carryforward period in the jurisdictions in which they arose. The following table provides detail surrounding the expiration dates of NOLs and other tax credit carryforwards before valuation allowances: Years Ending September 30 NOLs Credits (In millions) 2021 - 2027 $ 168 $ 50 2028 and thereafter 198 73 Indefinite carryforwards 287 2 Total $ 653 $ 125 As of September 30, 2020, provisions have not been made for non-U.S. withholding taxes or other applicable taxes on $1,631 million of undistributed earnings of non-U.S. subsidiaries, as these earnings are considered indefinitely reinvested. It is not practicable to calculate the unrecognized deferred tax liability on undistributed earnings. Cabot continually reviews the financial position and forecasted cash flows of its U.S. consolidated group and foreign subsidiaries in order to reaffirm the Company’s intent and ability to continue to indefinitely reinvest earnings of its foreign subsidiaries or whether such earnings will need to be repatriated in the foreseeable future. Such review encompasses operational needs and future capital investments. From time to time, however, the Company’s intentions relative to specific indefinitely reinvested amounts change because of certain unique circumstances. These earnings could become subject to non-U.S. withholding taxes and other applicable taxes if they were remitted to the U.S. Cabot has filed its tax returns in accordance with the tax laws in each jurisdiction and recognizes tax benefits for uncertain tax positions when the position would more likely than not be sustained based on its technical merits and recognizes measurement adjustments when needed. As of September 30, 2020, the total amount of unrecognized tax benefits was $23 million, of which $14 million was recorded in the Company’s Consolidated Balance Sheets and $9 million of deferred tax assets, principally related to state NOLs, have not been recorded. In addition, accruals of $1 million and $3 million have been recorded for penalties and interest, respectively, as of September 30, 2020. Total penalties and interest recorded in the tax provision in the Consolidated Statements of Operations was $1 million in fiscal 2020, and $2 million in both 2019 and 2018. If the unrecognized tax benefits were recognized at a given point in time, there would be $23 million favorable impact on the Company’s tax provision before consideration of the impact of the potential need for valuation allowances. A reconciliation of the beginning and ending amount of unrecognized tax benefits for fiscal 2020, 2019 and 2018 is as follows: Years Ended September 30 2020 2019 2018 (In millions) Balance at beginning of the year $ 27 $ 37 $ 36 Additions based on tax provisions related to the current year 2 — 2 Additions for tax positions of prior years 2 — 1 Reductions of tax provisions of prior years (1 ) (1 ) — Reductions related to settlements (5 ) (5 ) — Reductions from lapse of statute of limitations (2 ) (4 ) (2 ) Balance at end of the year $ 23 $ 27 $ 37 Cabot and certain subsidiaries are under audit in a number of jurisdictions. In addition, certain statutes of limitations are scheduled to expire in the near future. It is reasonably possible that a further change in the unrecognized tax benefits may occur within the next twelve months related to the settlement of one or more of these audits or the lapse of applicable statutes of limitations; however, an estimated range of the impact on the unrecognized tax benefits cannot be quantified at this time. Cabot files U.S. federal and state and non-U.S. income tax returns in jurisdictions with varying statutes of limitations. The 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 significant

Leases

Leases	12 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Leases	Note T. Leases The Company determines if an arrangement is a lease at inception. The Company considers a contract to be or to contain a lease if the contract conveys the right to control the use of identified property, plant, or equipment (an identified asset) for a period of time in exchange for consideration. A lease liability is recorded at commencement for the net present value of future lease payments over the lease term. The discount rate used is generally the Company’s estimated incremental borrowing rate based on credit-adjusted and term-specific discount rates, using a third-party yield curve. An ROU asset is recorded and recognized at commencement at the lease liability amount, including initial direct costs incurred, and is reduced for lease incentives received. The Company’s lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise that option. In the normal course of its business, the Company enters into various leases as the lessee, primarily related to certain transportation vehicles, warehouse facilities, office space, and machinery and equipment. These leases have remaining lease terms between one and nineteen years, some of which may include options to extend the leases for up to fifteen years or options to terminate the leases. The Company’s land leases have remaining lease terms up to seventy years. Some lease arrangements require variable payments that are dependent on usage, output, or index-based adjustments. The Company does not have material variable lease payments. The Company has elected not to recognize short-term leases on the balance sheet for all underlying asset classes. Short-term leases are leases that, at the commencement date, have a lease term of twelve months or less and do not include a purchase option that the Company is reasonably certain to exercise. Short-term leases are expensed on a straight-line basis over the lease term. The components of the Company’s lease costs were as follows: Year Ended September 30 2020 (In millions) Operating lease cost $ 32 Finance lease cost 6 Total lease cost $ 38 For fiscal 2020, short-term lease costs were $6 million, and variable lease costs were $1 million. Supplemental cash flow information related to the Company’s leases was as follows: Year Ended September 30 2020 (In millions) Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 25 Operating cash flows from finance leases 2 Financing cash flows from finance leases 3 Right-of-use assets obtained in exchange for new operating lease liabilities $ 14 Right-of-use assets obtained in exchange for new finance lease liabilities $ 24 Supplemental balance sheet information related to the Company’s leases was as follows: Description Balance Sheet Classification September 30, 2020 (In millions) Lease ROU assets: Operating Other assets $ 98 Finance Net property, plant and equipment 44 Total lease ROU assets $ 142 Lease liabilities: Current: Operating Accounts payable and accrued liabilities $ 15 Finance Current portion of long-term debt 3 Long-term: Operating Other liabilities 89 Finance Long-term debt 28 Total lease liabilities $ 135 The following table presents the weighted-average remaining lease term and discount rates for the Company’s leases as of September 30, 2020: Description September 30, 2020 Weighted-average remaining lease term (years): Operating leases 17 Finance leases 12 Weighted-average discount rate: Operating leases 2.19 % Finance leases 4.42 % Future minimum lease payments under non-cancelable operating and finance leases as of September 30, 2020 were as follows: Years Ended September 30 Operating leases Finance leases (In millions) 2021 $ 17 $ 5 2022 12 4 2023 11 4 2024 10 4 2025 9 4 2026 and thereafter 67 19 Total lease payments 126 40 Less: imputed interest 22 9 Total $ 104 $ 31 The Company’s future minimum lease payments under non-cancelable leases as of September 30, 2019 were as follows: Years Ended September 30 Operating leases Capital leases (In millions) 2020 $ 23 $ 3 2021 14 3 2022 9 3 2023 9 3 2024 8 2 2025 and thereafter 68 7 Total lease payments 131 21 Less: imputed interest — 9 Total $ 131 $ 12

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note U. Commitments and Contingencies Other Long-Term Commitments Cabot has entered into long-term purchase agreements primarily for the purchase of raw materials. Under certain of these agreements, the quantity of material being purchased is fixed, but the price paid changes as market prices change. Raw materials purchased under these agreements by segment for fiscal 2020, 2019 and 2018 are as follows: Years Ended September 30 2020 2019 2018 (In millions) Reinforcement Materials $ 198 $ 393 $ 375 Performance Chemicals 58 65 55 Purification Solutions 2 8 11 Total $ 258 $ 466 $ 441 Included in the table above are raw materials purchases from noncontrolling shareholders of consolidated subsidiaries. These purchases were $81 million during fiscal 2020 and $156 million during both fiscal 2019 and fiscal 2018, and accounts payable and accrued liabilities owed to noncontrolling shareholders as of September 30, 2020 and 2019, were $ 12 For these purchase commitments, the amounts included in the table below are based on market prices as of September 30, 2020 which may differ from actual market prices at the time of purchase. Payments Due by Fiscal Year 2021 2022 2023 2024 2025 Thereafter Total (In millions) Reinforcement Materials $ 115 $ 101 $ 87 $ 86 $ 86 $ 911 $ 1,386 Performance Chemicals 54 53 34 34 35 332 $ 542 Total $ 169 $ 154 $ 121 $ 120 $ 121 $ 1,243 $ 1,928 The Company has also entered into long-term purchase agreements primarily for services related to information technology, which are not included in the table above, that total $ 14 Guarantee Agreements Cabot has provided certain indemnities pursuant to which it may be required to make payments to an indemnified party in connection with certain transactions and agreements. In connection with certain acquisitions and divestitures, Cabot has provided routine indemnities with respect to such matters as environmental, tax, insurance, product and employee liabilities. In connection with various other agreements, including service and supply agreements with customers, Cabot has provided indemnities for certain contingencies and routine warranties. Cabot is unable to estimate the maximum potential liability for these types of indemnities as a maximum obligation is not explicitly stated in most cases and the amounts, if any, are dependent upon the outcome of future contingent events, the nature and likelihood of which cannot be reasonably estimated. The duration of the indemnities vary, and in many cases are indefinite. Cabot has not recorded any liability for these indemnities in the consolidated financial statements, except as otherwise disclosed. Self-Insurance and Retention for Certain Contingencies The Company is partially self-insured for certain third-party liabilities globally, as well as workers’ compensation and employee medical benefits in the United States. The third-party and workers’ compensation liabilities are managed through a wholly-owned insurance captive and the related liabilities are included in the consolidated financial statements. The employee medical obligations are managed by a third-party provider and the related liabilities are included in the consolidated financial statements. To limit Cabot’s potential liabilities for these risks, however, the Company purchases insurance from third-parties that provides stop-loss protection. The self-insured liability in fiscal 2020 for third-party liabilities was $500,000 per accident for auto, $2 million per occurrence for all other, $1 million per accident for U.S. workers’ compensation, and the retention for medical costs in the United States is at most $250,000 per person per annum. Contingencies Cabot is a defendant, or potentially responsible party, in various lawsuits and environmental proceedings wherein substantial amounts are claimed or at issue. Environmental Matters As of September 30, 2020 and 2019, Cabot had $ 7 3 4 Charges for environmental expense were $ 1 7 The operation and maintenance component of the $ 7 4 In November 2013, Cabot entered into a Consent Decree with the EPA and the Louisiana Department of Environmental Quality (“LDEQ”) regarding Cabot’s three carbon black manufacturing facilities in the U.S. This settlement is related to EPA’s national enforcement initiative focused on the U.S. carbon black manufacturing sector alleging non-compliance with certain regulatory and permitting requirements under The Clean Air Act, including the New Source Review (“NSR”) construction permitting requirements. Pursuant to this settlement, Cabot is in the process of installing technology controls for the reduction of sulfur dioxide and nitrogen oxide emissions at certain of its carbon black plants. Respirator Liabilities Cabot has exposure in connection with a safety respiratory products business that a subsidiary acquired from American Optical Corporation (“AO”) in an April 1990 asset purchase transaction. The subsidiary manufactured respirators under the AO brand and disposed of that business in July 1995. In connection with its acquisition of the business, the subsidiary agreed, in certain circumstances, to assume a portion of AO’s liabilities, including costs of legal fees together with amounts paid in settlements and judgments, allocable to AO respiratory products used prior to the 1990 purchase by the Cabot subsidiary. In exchange for the subsidiary’s assumption of certain of AO’s respirator liabilities, AO agreed to provide to the subsidiary the benefits of: (i) AO’s insurance coverage for the period prior to the 1990 acquisition and (ii) a former owner’s indemnity of AO holding it harmless from any liability allocable to AO respiratory products used prior to May 1982. Generally, these respirator liabilities involve claims for personal injury, including asbestosis, silicosis and coal worker’s pneumoconiosis, allegedly resulting from the use of respirators that are alleged to have been negligently designed and/or labeled. At no time did this respiratory product line represent a significant portion of the respirator market. The subsidiary transferred the business to Aearo Corporation (“Aearo”) in July 1995. Cabot agreed to have the subsidiary retain certain liabilities associated with exposure to asbestos and silica while using respirators prior to the 1995 transaction so long as Aearo paid, and continues to pay, Cabot an annual fee of $400,000. Aearo can discontinue payment of the fee at any time, in which case it will assume the responsibility for and indemnify Cabot against those liabilities which Cabot’s subsidiary had agreed to retain. The Company anticipates that it will continue to receive payment of the $400,000 fee from Aearo and thereby retain these liabilities for the foreseeable future. Cabot has no liability in connection with any products manufactured by Aearo after 1995. In addition to Cabot’s subsidiary and as described above, other parties are responsible for significant portions of the costs of respirator liabilities, leaving Cabot’s subsidiary with a portion of the liability in only some of the pending cases. These parties include Aearo, AO, AO’s insurers, another former owner and its insurers and a third-party manufacturer of respirators formerly sold under the AO brand and its insurers (collectively, with the Company’s subsidiary, the “Payor Group”). Cabot has contributed to the Payor Group’s defense and settlement costs with respect to a percentage of pending claims depending on several factors, including the period of alleged product use. In order to quantify Cabot’s estimated share of liability for pending and future respirator liability claims, Cabot has engaged, through counsel, the assistance of Nathan Associates, Inc. (“Nathan”), a leading consulting firm in the field of tort liability valuation. The methodology used to estimate the liability addresses the complexities surrounding Cabot’s potential liability by making assumptions based on the Company’s experience with these claims about Cabot’s likely exposure related to claims pending for less than 10 years, the viability of pending claims, and the estimated number of future claimants with respect to periods of asbestos, silica and coal mine dust exposure and respirator use. Using those and other assumptions, the Company estimates the costs that would be incurred in defending and resolving both currently pending and future claims. During fiscal 2020, the Company updated this estimate with the assistance of Nathan. Based on the updated estimate, the Company updated its reserve as of September 30, 2020 for Cabot’s estimated share of the liability for pending and future respirator claims and recorded a charge of $3 million, which is included in Selling and administrative expenses in the Consolidated Statements of Operations. This reserve reflects higher costs of defending and resolving these claims. Based on these estimates, as of September 30, 2020 and 2019, the Company had $24 million and $35 million, respectively, reserved for its estimated share of liability for pending and future respirator 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. In February 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 is $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 this settlement in the third quarter of fiscal 2020. The remaining $32.6 million is included in Accounts payable and accrued liabilities on the Consolidated Balance Sheets as of September 30, 2020 and was paid by the Company in the first quarter of fiscal 2021. In fiscal 2019 and 2018, the Company recorded charges of $20 million and $10 million, respectively, related to the respirator liability which was included in Selling and administrative expenses in the Consolidated Statements of Operations. In addition to the settlement noted above, the Company made payments related to its respirator liability of $4 million in fiscal 2020, $10 million in fiscal 2019 and $3 million in fiscal 2018. The Company’s current estimate of the cost of its share of existing and future respirator liability claims is based on facts and circumstances existing at this time, including the number and nature of the remaining claims. Developments that could affect the Company’s estimate include, but are not limited to, (i) significant changes in the number of future claims, (ii) changes in the rate of dismissals without payment of pending claims, (iii) significant changes in the average cost of resolving claims, including potential settlements of groups of claims, (iv) significant changes in the legal costs of defending these claims, (v) changes in the nature of claims received 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 existing and future claims could be different than the reserved amount. Value-added Tax (“VAT”) Matter The Company has received assessments from a non-U.S. taxing authority for VAT related to certain sales made and services provided by certain of the Company’s subsidiaries from 2014 through 2019. The Company believes these transactions are exempt from VAT and has filed legal actions challenging the taxing authority’s application of VAT to them. Hearings on these matters are ongoing and it will likely be a number of years before they are resolved. The Company believes its interpretation of these VAT rules is appropriate, and that it will be successful in its challenge against the taxing authority’s assessments. Accordingly, the Company does not believe it is probable that it will incur a loss related to these matters. However, the interpretation and application of these VAT rules is an unsettled issue, and the resolution of tax and regulatory matters is unpredictable. If it is determined in these proceedings that VAT applies to some or all of these various transactions, the Company could incur a charge that ranges between nil and $30 million for these matters, with the amount impacted by any interest and penalties associated with these matters and the amount, if any, of VAT the Company might subsequently recover from its customers. Other Matters The Company has various other lawsuits, claims and contingent liabilities arising in the ordinary course of its business and with respect to its divested businesses. The Company does not believe that any of these matters will have a material adverse effect on its financial position; however, litigation is inherently unpredictable. Cabot could incur judgments, enter into settlements or revise its expectations regarding the outcome of certain matters, and such developments could have a material impact on its results of operations in the period in which the amounts are accrued or its cash flows in the period in which the amounts are paid.

Financial Information by Segmen

Financial Information by Segment & Geographic Area	12 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Financial Information by Segment & Geographic Area	Note V. Financial Information by Segment & Geographic Area Segment Information The Company identifies a business as an operating segment if: i) it engages in business activities from which it may earn revenues and incur expenses; ii) its operating results are regularly reviewed by the Chief Operating Decision Maker (“CODM”), who is Cabot’s President and Chief Executive Officer, to make decisions about resources to be allocated to the segment and assess its performance; and iii) it has available discrete financial information. The Company has determined that all of its businesses are operating segments. The CODM reviews financial information at the operating segment level to allocate resources and to assess the operating results and financial performance for each operating segment. Operating segments are aggregated into a reportable segment if the operating segments are determined to have similar economic characteristics and if the operating segments are similar in the following areas: i) nature of products and services; ii) nature of production processes; iii) type or class of customer for their products and services; iv) methods used to distribute the products or provide services; and v) if applicable, the nature of the regulatory environment. The Company has three reportable segments: Reinforcement Materials, Performance Chemicals and Purification Solutions. The Company’s former Specialty Fluids business was a The Reinforcement Materials segment combines the rubber blacks and engineered elastomer composites product lines. The Performance Chemicals segment combines the specialty grades of carbon black, fumed metal oxides and aerogel product lines into the Performance Additives business, and combines the specialty compounds and inkjet colorants product lines into the Formulated Solutions business. These businesses are similar in terms of economic characteristics, nature of products, processes, customer class and product distribution methods, and therefore have been aggregated into one reportable segment. The Purification Solutions segment represents the Company’s activated carbon business. Income (loss) from continuing operations before income taxes (“Segment EBIT”) is presented for each reportable segment in the financial information by the reportable segment table below on the line entitled Income (loss) from continuing operations before taxes. Segment EBIT excludes certain items, meaning items management does not consider representative of on-going operating segment results. In addition, Segment EBIT includes Equity in earnings of affiliated companies, net of tax, the full operating results of a contractual joint venture in Purification Solutions, royalties, Net income (loss) attributable to noncontrolling interests, net of tax, and discounting charges for certain Notes receivable, but excludes Interest expense, foreign currency transaction gains and losses, interest income, dividend income, unearned revenue, general unallocated expense and unallocated corporate costs. Segment assets exclude cash, short-term investments, cost investments, income taxes receivable, deferred taxes and headquarters’ assets, which are included in unallocated and other. Expenditures for additions to long-lived assets include total equity and other investments (including available-for-sale securities) and property, plant and equipment. Reinforcement Materials Carbon black is a form of elemental carbon that is manufactured in a highly controlled process to produce particles and aggregates of varied structure and surface chemistry, resulting in many different performance characteristics for a wide variety of applications. Rubber grade carbon blacks are used to enhance the physical properties of the systems and applications in which they are incorporated. The Company’s rubber blacks products are used in tires and industrial products. Rubber blacks have traditionally been used in the tire industry as a rubber reinforcing agent to increase tread durability and are also used as a performance additive to reduce rolling resistance and improve traction. In industrial products such as hoses, belts, extruded profiles and molded goods, rubber blacks are used to improve the physical performance of the product, including the product’s physical strength, fluid resistance, conductivity and resistivity. In addition to its rubber blacks products, the Company manufactures engineered elastomer composites (“E2C™”) solutions that are compounds of carbon black and rubber using its patented elastomer composites manufacturing process. These compounds improve abrasion/wear resistance, reduce fatigue of rubber parts and reduce rolling resistance compared to carbon black/rubber compounds made by conventional dry mix methods enabling rubber compounders to break (or, reduce the need to make) performance trade-offs. Performance Chemicals Performance Chemicals is organized into two businesses: the Company’s Performance Additives business and its Formulated Solutions business. The Company’s Performance Additives business combines its specialty grades of carbon black, fumed metal oxides and aerogel product lines, and its Formulated Solutions business combines its specialty compounds and inkjet product lines. In Performance Chemicals, the Company designs, manufactures and sells materials that deliver performance in a broad range of customer applications across the automotive, construction, infrastructure, inkjet printing, electronics, and consumer products sectors, and applications related to generation, transmission and storage of energy. The Company’s focus areas for growth include carbon additives and other materials for battery applications, inkjet inks and dispersions for post print corrugated packaging applications, and conductive compounds for various plastics applications. The net sales from each of these businesses for fiscal 2020, 2019 and 2018 are as follows: Years Ended September 30 2020 2019 2018 (In millions) Performance Additives $ 645 $ 694 $ 707 Formulated Solutions 288 301 321 Total Performance Chemicals $ 933 $ 995 $ 1,028 Performance Additives Business The Company’s specialty grades of carbon black are used to impart color, provide rheology control, enhance conductivity and static charge control, provide UV protection, enhance mechanical properties, and provide formulation flexibility through surface treatment. These specialty carbon products are used in a wide variety of applications, such as inks, coatings, cables, plastics, adhesives, toners, batteries and displays. Fumed silica is an ultra-fine, high-purity particle used as a reinforcing, thickening, abrasive, thixotropic, suspending or anti-caking agent in a wide variety of products for the automotive, construction, microelectronics, batteries, and consumer products industries. These products include adhesives, sealants, cosmetics, batteries, inks, toners, silicone elastomers, coatings, polishing slurries and pharmaceuticals. Fumed alumina, also an ultra-fine, high-purity particle, is used as an abrasive, absorbent or barrier agent in a variety of products, such as inkjet media, lighting, coatings, cosmetics and polishing slurries. Aerogel is a hydrophobic, silica-based particle with a high surface area that is used in a variety of thermal insulation and specialty chemical applications. In the building and construction industry, the product is used in insulative sprayable plasters and composite building products, as well as translucent skylight, window, wall and roof systems for insulating eco-daylighting applications. In the specialty chemicals industry, the product is used to provide matte finishing, insulating and thickening properties for use in a variety of applications. Formulated Solutions Business Cabot’s masterbatch and conductive compound products, which Cabot refers to as “specialty compounds”, are formulations derived from specialty grades of carbon black mixed with polymers and other additives. These products are generally used by plastic resin producers and converters in applications for the automotive, industrial, packaging, infrastructure, agricultural, consumer products, and electronics industries. As an alternative to directly mixing specialty carbon blacks, these formulations offer greater ease of handling and help customers achieve their desired levels of dispersion and color and manage the addition of small doses of additives. In addition, Cabot’s electrically conductive compound products generally are used to help ensure uniform conductive performance and reduce risks associated with electrostatic discharge in plastics applications. The Company’s inkjet colorants are high-quality pigment-based black and color dispersions based on its patented carbon black surface modification technology. The dispersions are used in aqueous inkjet inks to impart color, sharp print characteristics and durability, while maintaining high printhead reliability. These products are used in various inkjet printing applications, including commercial printing, small office/home office and corporate office, that require a high level of dispersibility and colloidal stability. Cabot’s inkjet inks, which utilize its pigment-based colorant dispersions, are used in the commercial printing segment for digital print. Purification Solutions The Company’s activated carbon products are used for the purification of water, air, food and beverages, pharmaceuticals and other liquids and gases, as either a colorant or a decolorizing agent in the production of products for food and beverage applications and as a chemical carrier in slow release applications. In gas and air applications, one of the uses of activated carbon is for the removal of mercury in flue gas streams. In certain applications, used activated carbon can be reactivated for further use by removing the contaminants from the pores of the activated carbon product. The most common applications for the Company’s reactivated carbon are water treatment and food and beverage purification. In addition to activated carbon production and reactivation, the Company also provides activated carbon solutions through on-site equipment and services, including delivery systems for activated carbon injection in coal-fired utilities, mobile water filter units and carbon reactivation services. Specialty Fluids Cabot divested its Specialty Fluids business on June 28, 2019. Refer to Note D for the terms of this transaction. The Specialty Fluids segment produced and marketed a range of cesium products that included cesium formate brines and other fine cesium chemicals. Financial information by reportable segment is as follows: Years Ended September 30 Reinforcement Materials Performance Chemicals Purification Solutions Specialty Fluids Segment Total (1) Unallocated and Other (2), (4) Consolidated Total (In millions) 2020 Revenues from external customers (3) $ 1,256 $ 933 $ 253 $ — $ 2,442 $ 172 $ 2,614 Depreciation and amortization $ 68 $ 64 $ 24 $ — $ 156 $ 2 $ 158 Equity in earnings of affiliated companies $ — $ 1 $ 3 $ — $ 4 $ (1 ) $ 3 Income (loss) from continuing operations before income taxes (4) $ 162 $ 118 $ 3 $ — $ 283 $ (316 ) $ (33 ) Assets (5) $ 1,077 $ 1,145 $ 296 $ — $ 2,518 $ 263 $ 2,781 Total expenditures for additions to long-lived assets (6) $ 66 $ 92 $ 8 $ — $ 166 $ 3 $ 169 2019 Revenues from external customers (3) $ 1,815 $ 995 $ 278 $ 56 $ 3,144 $ 193 $ 3,337 Depreciation and amortization $ 69 $ 51 $ 26 $ 1 $ 147 $ 1 $ 148 Equity in earnings of affiliated companies $ (1 ) $ 1 $ 3 $ — $ 3 $ (2 ) $ 1 Income (loss) from continuing operations before income taxes (4) $ 266 $ 152 $ 2 $ 24 $ 444 $ (189 ) $ 255 Assets (5) $ 1,177 $ 1,024 $ 436 $ — $ 2,637 $ 367 $ 3,004 Total expenditures for additions to long-lived assets (6) $ 82 $ 148 $ 11 $ 1 $ 242 $ 5 $ 247 2018 Revenues from external customers (3) $ 1,774 $ 1,028 $ 279 $ 45 $ 3,126 $ 116 $ 3,242 Depreciation and amortization $ 70 $ 48 $ 32 $ 2 $ 152 $ (3 ) $ 149 Equity in earnings of affiliated companies $ 1 $ — $ 6 $ — $ 7 $ (5 ) $ 2 Income (loss) from continuing operations before income taxes (4) $ 279 $ 200 $ (7 ) $ 8 $ 480 $ (363 ) $ 117 Assets (5) $ 1,319 $ 919 $ 460 $ 178 $ 2,876 $ 368 $ 3,244 Total expenditures for additions to long-lived assets (6) $ 97 $ 94 $ 16 $ 17 $ 224 $ 5 $ 229 (1) Cabot divested its Specialty Fluids business on June 28, 2019. Refer to Note D for the terms of this transaction. (2) Unallocated and Other includes certain items and eliminations necessary to reflect management’s reporting of operating segment results. These items are reflective of the segment reporting presented to the CODM. ( 3 ) Consolidated Total Revenues from external customers reconciles to Net sales and other operating revenues on the Consolidated Statements of Operations. Revenues from external customers that are categorized as Unallocated and Other reflects royalties, external shipping and handling fees, the impact of unearned revenue, the removal of 100 % of the sales of an equity method affiliate and discounting charges for certain Notes receivable. Details are provided in the table below. Years Ended September 30 2020 2019 2018 (In millions) Royalties, the impact of unearned revenue, the removal of 100% discounting charges for certain Notes receivable $ (3 ) $ (13 ) $ 11 Shipping and handling fees 113 130 105 By-product sales (a) 62 76 — Total $ 172 $ 193 $ 116 (a) Revenue from Contracts with Customers ( 4 ) Consolidated Total Income (loss) from continuing operations before income taxes reconciles to Income (loss) from continuing operations before income taxes and equity in earnings of affiliated companies on the Consolidated Statements of Operations. Total Income (loss) from continuing operations before income taxes that are categorized as Unallocated and Other includes: Years Ended September 30 2020 2019 2018 (In millions) Interest expense $ (53 ) $ (59 ) $ (54 ) Certain items: (a) Marshall Mine loss on sale and asset impairment charge (Note D) $ (129 ) $ — $ — Legal and environmental matters and reserves (Note U) (54 ) (21 ) (16 ) Global restructuring activities (Note P) (19 ) (16 ) 30 Employee benefit plan settlement and other charges (Note N) (10 ) 1 — Acquisition and integration-related charges (Note C) (5 ) (6 ) (2 ) Inventory reserve adjustment (2 ) — (13 ) Specialty Fluids loss on sale and asset impairment charge (Note D) (1 ) (29 ) — Equity affiliate investment impairment charge (Note M) — (11 ) — Executive transition costs — (1 ) (2 ) Indirect tax settlement credits 3 — — Purification Solutions goodwill and long-lived assets impairment charge (Note G) — — (254 ) Gains (losses) on sale of investments — — 10 Other certain items (1 ) (4 ) (1 ) Total certain items, pre-tax (218 ) (87 ) (248 ) Unallocated corporate costs (b) (41 ) (50 ) (61 ) General unallocated income (expense) (c) (1 ) 8 2 Less: Equity in earnings of affiliated companies, net of tax (d) 3 1 2 Total $ (316 ) $ (189 ) $ (363 ) (a) Certain items are items that management does not consider representative of operating segment results and they are, therefore, excluded from Segment EBIT. (b) Unallocated corporate costs are not controlled by the segments and primarily benefit corporate interests. (c) General unallocated income (expense) consists of gains (losses) arising from foreign currency transactions, net of other foreign currency risk management activities, interest income, dividend income, the profit or loss related to the corporate adjustment for unearned revenue, and the impact of including the full operating results of a contractual joint venture in Purification Solutions Segment EBIT. (d) Equity in earnings of affiliated companies, net of tax is included in Segment EBIT and is removed from Unallocated and other to reconcile to income (loss) from operations before taxes. ( 5 ) Unallocated and Other assets includes cash, marketable securities, cost investments, income taxes receivable, deferred taxes, headquarters’ assets, and current and non-current assets held for sale. ( 6 ) Expenditures for additions to long-lived assets include total equity and other investments (including available-for-sale securities) and property, plant and equipment. Geographic Information Revenues from external customers attributable to an individual country, other than the U.S. and China, were not material for disclosure. Revenues from external customers by individual country are summarized as follows: Years Ended September 30 2020 2019 2018 (In millions) United States $ 581 $ 702 $ 676 China 598 738 752 Other countries 1,435 1,897 1,814 Total $ 2,614 $ 3,337 $ 3,242 Each of the Company’s segments operate globally. In addition to presenting Revenue from external customers by reportable segment, the following tables further disaggregate Revenue from external customers by geographic region. Year Ended September 30, 2020 Reinforcement Materials Performance Chemicals Purification Solutions Consolidated Total (In millions) Americas $ 490 $ 266 $ 112 $ 868 Asia Pacific 529 368 34 931 Europe, Middle East and Africa 237 299 107 643 Segment revenues from external customers 1,256 933 253 2,442 Unallocated and other 172 Net sales and other operating revenues $ 2,614 Year Ended September 30, 2019 Reinforcement Materials Performance Chemicals Purification Solutions Specialty Fluids Consolidated Total (In millions) Americas $ 688 $ 294 $ 126 $ 6 $ 1,114 Asia Pacific 769 353 35 1 1,158 Europe, Middle East and Africa 358 348 117 49 872 Segment revenues from external customers 1,815 995 278 56 3,144 Unallocated and other 193 Net sales and other operating revenues $ 3,337 Long-lived assets attributable to an individual country, other than the U.S. and China, were not material for disclosure. Long-lived asset information by individual country is summarized as follows: Years Ended September 30 2020 2019 2018 (In millions) United States $ 493 $ 572 $ 493 China 295 264 270 Other countries 526 512 533 Total $ 1,314 $ 1,348 $ 1,296

Unaudited Quarterly Financial I

Unaudited Quarterly Financial Information	12 Months Ended
	Sep. 30, 2020
Quarterly Financial Information Disclosure [Abstract]
Unaudited Quarterly Financial Information	Note W. Unaudited Quarterly Financial Information Unaudited financial results by quarter for fiscal 2020 and 2019 are summarized below: Quarters Ended Year Ended December 31, March 31, June 30, September 30, September 30, 2019 2020 2020 2020 2020 (In millions, except per share amounts) Net sales and other operating revenues $ 727 $ 710 $ 518 $ 659 $ 2,614 Gross profit $ 141 $ 153 $ 69 $ 137 $ 500 Net income (loss) $ 46 $ 3 $ (5 ) $ (265 ) $ (221 ) Net income (loss) attributable to Cabot Corporation $ 41 $ (1 ) $ (6 ) $ (272 ) $ (238 ) Earnings per common share—basic $ 0.71 $ (0.01 ) $ (0.12 ) $ (4.81 ) $ (4.21 ) Earnings per common share—diluted $ 0.70 $ (0.01 ) $ (0.12 ) $ (4.81 ) $ (4.21 ) During the fourth quarter of fiscal 2020, Cabot recorded a pre-tax charge of $129 million related to its sale of the Marshall Mine as discussed further in Note D and a $228 million charge due to a valuation allowance increase as discussed in Note S. Quarters Ended Year Ended December 31, March 31, June 30, September 30, September 30, 2018 2019 2019 2019 2019 (In millions, except per share amounts) Net sales and other operating revenues $ 821 $ 844 $ 845 $ 827 $ 3,337 Gross profit $ 166 $ 178 $ 170 $ 171 $ 685 Net income (loss) $ 77 $ 29 $ 40 $ 40 $ 186 Net income (loss) attributable to Cabot Corporation $ 69 $ 23 $ 32 $ 33 $ 157 Earnings per common share—basic $ 1.14 $ 0.39 $ 0.55 $ 0.56 $ 2.64 Earnings per common share—diluted $ 1.14 $ 0.39 $ 0.55 $ 0.55 $ 2.63 During the fourth quarter of fiscal 2019, Cabot recorded a pre-tax charge of $20 million related to its respirator liabilities as discussed further in Note U.

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of Cabot and its wholly-owned subsidiaries and majority-owned and controlled U.S. and non-U.S. subsidiaries. Additionally, Cabot considers consolidation of entities over which control is achieved through means other than voting rights, of which there were none in the periods presented. Intercompany transactions have been eliminated in consolidation.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash equivalents include all highly liquid investments with a maturity of three months or less at date of acquisition. Cabot continually assesses the liquidity of cash equivalents and, as of September 30, 2020, has determined that they are readily convertible to cash.
Inventories	Inventories Inventories are stated at the lower of cost or net realizable value. The cost of inventories is determined using the first-in, first-out method. Cabot periodically reviews inventory for both potential obsolescence and potential declines in anticipated selling prices. In this review, the Company makes assumptions about the future demand for and market value of the inventory, and based on these assumptions estimates the amount of any obsolete, unmarketable, slow moving, or overvalued inventory. Cabot writes down the value of these inventories by an amount equal to the difference between the cost of the inventory and its estimated net realizable value.
Investments	Investments The Company has investments in equity affiliates and marketable securities. As circumstances warrant, all investments are subject to periodic impairment reviews. Unless consolidation is required, investments in equity affiliates, where Cabot generally owns between 20% and 50% of the affiliate, are accounted for using the equity method. Cabot records its share of the equity affiliate’s results of operations based on its percentage of ownership of the affiliate. Dividends declared from equity affiliates are a return on investment and are recorded as a reduction to the equity investment value. In the second quarter of fiscal 2019, the Company recorded an impairment charge of $11 million related to its Venezuelan equity investment, which is included in Other income (expense) within the Consolidated Statements of Operations. Refer to Note M for details related to the impairment charge. At both September 30, 2020 and 2019, Cabot had equity affiliate investments of $39 million
Intangible Assets and Goodwill Impairment	Intangible Assets and Goodwill Impairment The Company records tangible and intangible assets acquired and liabilities assumed in business combinations under the acquisition method of accounting. Amounts paid for an acquisition are allocated to the assets acquired and liabilities assumed based on their fair values at the date of acquisition. The Company uses assumptions and estimates in determining the fair value of assets acquired and liabilities assumed in a business combination. The determination of the fair value of intangible assets requires the use of significant judgment with regard to assumptions used in the valuation model. The Company estimates the fair value of identifiable acquisition-related intangible assets principally based on projections of cash flows that will arise from these assets. The projected cash flows are discounted to determine the fair value of the assets at the dates of acquisition. Definite-lived intangible assets, which are comprised of trademarks, customer relationships and developed technologies, are amortized over their estimated useful lives and are reviewed for impairment when indication of potential impairment exists, such as a significant reduction in cash flows associated with the assets. Goodwill is comprised of the purchase price of business acquisitions in excess of the fair value assigned to the net tangible and identifiable intangible assets acquired. Goodwill is not amortized and is subject to impairment testing annually, or when events or changes in the business environment indicate that the carrying value of the reporting unit may exceed its fair value. A reporting unit, for the purpose of the impairment test, is at or below the operating segment level, and constitutes a business for which discrete financial information is available and regularly reviewed by segment management. Reinforcement Materials, and the fumed metal oxides, specialty compounds, and specialty carbons product lines within Performance Chemicals, which are considered separate reporting units, carry the Company’s goodwill balances as of September 30, 2020. For the purpose of the goodwill impairment test, the Company first assesses qualitative factors to determine whether it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If an initial qualitative assessment identifies that it is more likely than not that the carrying value of a reporting unit exceeds its estimated fair value, an additional quantitative evaluation is performed. Alternatively, the Company may elect to proceed directly to the quantitative goodwill impairment test. If based on the quantitative evaluation the fair value of the reporting unit is less than its carrying amount, a goodwill impairment loss would result. The goodwill impairment loss would be the amount by which the carrying value of the reporting unit, including goodwill, exceeds its fair value, limited to the total amount of goodwill allocated to that reporting unit. The fair value of a reporting unit is based on discounted estimated future cash flows. The fair value is also benchmarked against the value calculated from a market approach using the guideline public company method. The assumptions used to estimate fair value include management’s best estimates of future growth rates, operating cash flows, capital expenditures and discount rates over an estimate of the remaining operating period at the reporting unit level. Based on the Company’s most recent annual goodwill impairment test performed as of August 31, 2020, the fair values of the Reinforcement Materials, Fumed Metal Oxides, Specialty Compounds, and Specialty Carbons reporting units were substantially in excess of their carrying values.
Long-Lived Assets Impairment	Long-lived Assets Impairment The Company’s long-lived assets primarily include property, plant and equipment, intangible assets, long-term investments and assets held for rent. The carrying values of long-lived assets are reviewed for impairment whenever events or changes in business circumstances indicate that the carrying amount of an asset may not be recoverable. To test for impairment of assets, the Company generally uses a probability-weighted estimate of the future undiscounted net cash flows of the assets over their remaining lives to determine if the value of the asset is recoverable. Long-lived assets are grouped with other assets and liabilities at the lowest level for which independent identifiable cash flows are determinable. An asset impairment is recognized when the carrying value of the asset is not recoverable based on the analysis described above, in which case the asset is written down to its fair value. If the asset does not have a readily determinable market value, a discounted cash flow model may be used to determine the fair value of the asset. In circumstances when an asset does not have separate identifiable cash flows, an impairment charge is recorded when the Company no longer intends to use the asset.
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment are recorded at cost. Depreciation of property, plant and equipment is calculated using the straight-line method over the estimated useful lives of the related assets. The depreciable lives for buildings, machinery and equipment, and other fixed assets are generally between twenty and twenty-five years, ten and twenty-five years, and three and twenty-five years, respectively. The cost and accumulated depreciation for property, plant and equipment sold, retired, or otherwise disposed of are removed from the Consolidated Balance Sheets and resulting gains or losses are included in earnings in the Consolidated Statements of Operations. Expenditures for repairs and maintenance are charged to expenses as incurred. Expenditures for major renewals and betterments, which significantly extend the useful lives of existing plant and equipment, are capitalized and depreciated. Cabot capitalizes interest costs when they are part of the cost of acquiring and constructing certain assets that require a period of time to prepare for their intended use. During fiscal 2020, 2019 and 2018, Cabot capitalized $2 million, $4 million and $2 million of interest costs, respectively. These amounts are amortized over the lives of the related assets when they are placed in service.
Asset Retirement Obligations	Asset Retirement Obligations Cabot estimates incremental costs for special handling, removal and disposal of materials that may or will give rise to conditional asset retirement obligations (“ARO”) and then discounts the expected costs back to the current year using a credit adjusted risk free rate. Cabot recognizes ARO liabilities and costs when the timing and/or settlement can be reasonably estimated. In certain instances, Cabot has not recorded a reserve for AROs because the timing of disposal of the underlying asset is unknown. The ARO reserves were $18 million and $26 million at September 30, 2020 and 2019, respectively, and are included in Accounts payable and accrued liabilities and Other liabilities on the Consolidated Balance Sheets. The decrease in the ARO reserve was due to the sale of Marshall Mine on September 30, 2020.
Foreign Currency Translation	Foreign Currency Translation The functional currency of the majority of Cabot’s foreign subsidiaries is the local currency in which the subsidiary operates. Assets and liabilities of foreign subsidiaries are translated into U.S. dollars at exchange rates in effect at the balance sheet dates. Income and expense items are translated at average monthly exchange rates during the year. Unrealized currency translation adjustments are included as a separate component of Accumulated other comprehensive income (loss) (“AOCI”) within stockholders’ equity. Realized and unrealized foreign currency gains and losses arising from transactions denominated in currencies other than the subsidiary’s functional currency are reflected in earnings with the exception of (i) intercompany transactions considered to be of a long-term investment nature; (ii) income taxes upon future repatriation of unremitted earnings from non-U.S. subsidiaries that are not indefinitely reinvested; and (iii) foreign currency borrowings designated as net investment hedges. Gains or losses arising from these transactions are included as a component of Other comprehensive income (loss). In fiscal 2020, 2019 and 2018, net foreign currency transaction loss of $6 million, Beginning July 1, 2018, the Argentina economy was determined to be highly inflationary. As a result, the functional currency of the Company’s Argentina subsidiary was changed to the U.S. dollar, Cabot’s reporting currency, which is discussed in Note M.
Share Repurchase	Share Repurchases Periodically, Cabot repurchases shares of the Company’s common stock in the open market or in privately negotiated transactions under the authorization approved by the Board of Directors as discussed in Item 5 under the heading “Issuer Purchases of Equity Securities”. The Company retires the repurchased shares and records the excess of the purchase price over par value to additional paid-in capital (“APIC”) until such amount is reduced to zero and then charges the remainder against retained earnings.
Financial Instruments	Financial Instruments Cabot’s financial instruments consist primarily of cash and cash equivalents, accounts and notes receivable, investments, accounts payable and accrued liabilities, short-term and long-term debt, and derivative instruments. The carrying values of Cabot’s financial instruments approximate fair value with the exception of fixed rate long-term debt, which is recorded at amortized cost. The fair values of the Company’s financial instruments are based on quoted market prices, if such prices are available. In situations where quoted market prices are not available, the Company relies on valuation models to derive fair value. Such valuation takes into account the ability of the financial counterparty to perform and the Company’s own credit risk. Cabot uses derivative financial instruments primarily for purposes of hedging the exposures to fluctuations in foreign currency exchange rates, which exist as part of its on-going business operations. Cabot does not enter into derivative contracts for speculative purposes, nor does it hold or issue any derivative contracts for trading purposes. All derivatives are recognized on the Consolidated Balance Sheets at fair value. Where Cabot has a legal right to offset derivative settlements under a master netting agreement with a counterparty, derivatives with that counterparty are presented on a net basis. The changes in the fair value of derivatives are recorded in either earnings or AOCI, depending on whether or not the instrument is designated as part of a hedge transaction and, if designated as part of a hedge transaction, the type of hedge transaction. The gains or losses on derivative instruments reported in AOCI are reclassified to earnings in the period in which earnings are affected by the underlying hedged item. The ineffective portion of all hedges is recognized in earnings during the period in which the ineffectiveness occurs. In accordance with Cabot’s risk management strategy, the Company may enter into certain derivative instruments that may not be designated as hedges for hedge accounting purposes. Although these derivatives are not designated as hedges, the Company believes that such instruments are closely correlated with the underlying exposure, thus managing the associated risk. The Company records in earnings the gains or losses from changes in the fair value of derivative instruments that are not designated as hedges. Cash movements associated with these instruments are presented in the Consolidated Statements of Cash Flows as Cash Flows from Operating Activities because the derivatives are designed to mitigate risk to the Company’s cash flow from operations.
Revenue Recognition	Revenue Recognition Cabot recognizes revenue when its customers obtain control of promised goods or services. The revenue recognized is the amount of consideration which the Company expects to receive in exchange for those goods or services. The Company’s contracts with customers are generally for products only and do not include other performance obligations. Generally, Cabot considers purchase orders, which in some cases are governed by master supply agreements, to be contracts with customers. The transaction price as specified on the purchase order or sales contract is considered the standalone selling price for each distinct product. To determine the transaction price at the time when revenue is recognized, the Company evaluates whether the price is subject to adjustments, such as for returns, discounts or volume rebates, which are stated in the customer contract, to determine the net consideration to which the Company expects to be entitled. Revenue from product sales is recognized based on a point in time model when control of the product is transferred to the customer, which typically occurs upon shipment or delivery of the product to the customer and title, risk and rewards of ownership have passed to the customer. The Company has an immaterial amount of revenue that is recognized over time. Payment terms typically range from zero to ninety days Shipping and handling activities that occur after the transfer of control to the customer are billed to customers and are recorded as sales revenue, as the Company considers these to be fulfillment costs. Shipping and handling costs are expensed in the period incurred and included in Cost of sales within the Consolidated Statement of Operations. Taxes collected on sales to customers are excluded from the transaction price. The Company generally provides a warranty that its products will substantially conform to the identified specifications. The Company’s liability typically is limited to either a credit equal to the purchase price or replacement of the non-conforming product. Returns under warranty have historically been immaterial. The Company does not have contract assets or liabilities that are material. As permitted by the revenue recognition standard, Revenue from Contracts with Customers
Cost of Sales	Cost of Sales Cost of sales consists of the cost of raw and packaging materials, direct manufacturing costs, depreciation, internal transfer costs, inspection costs, inbound and outbound freight and shipping and handling costs, plant purchasing and receiving costs and other overhead expenses necessary to manufacture the products.
Accounts and Notes Receivable	Accounts and Notes Receivable Trade receivables are recorded at the invoiced amount and generally do not bear interest. Trade receivables in China may at certain times be settled with the receipt of bank issued non-interest bearing notes. These notes totaled 34 Cabot maintains allowances for doubtful accounts based on an assessment of the collectability of specific customer accounts, the aging of accounts receivable and other economic information on both a historical and prospective basis. Customer account balances are charged against the allowance when it is probable the receivable will not be recovered. There were no material changes in the allowance for any of the years presented. There is no material off-balance sheet credit exposure related to customer receivable balances.
Stock-Based Compensation	Stock-based Compensation Cabot recognizes compensation expense for stock-based awards granted to employees using the fair value method. Under the fair value recognition provisions, stock-based compensation cost is measured at the grant date based on the fair value of the award, and is recognized as expense over the service period, which generally represents the vesting period, and includes an estimate of what level of performance the Company will achieve for Cabot’s performance-based stock awards. Cabot calculates the fair value of its stock options using the Black-Scholes option pricing model. The fair value of restricted stock units is determined using the closing price of Cabot stock on the day of the grant. The Company recognizes forfeitures as they occur.
Selling and Administrative Expenses	Selling and Administrative Expenses Selling and administrative expenses consist of salaries and fringe benefits of sales and office personnel, general office expenses and other expenses not directly related to manufacturing operations.
Research and Technical Expenses	Research and Technical Expenses Research and technical expenses include salaries, equipment and material expenditures, and contractor fees and are expensed as incurred.
Pensions and Other Postretirement Benefits	Pensions and Other Postretirement Benefits The Company recognizes the funded status of defined benefit pension and other postretirement benefit plans as an asset or liability. This amount is defined as the difference between the fair value of plan assets and the benefit obligation. Pension and post-retirement benefit costs other than service cost are included in Other income (expense) in the Consolidated Statement of Operations. The Company is required to recognize as a component of Other comprehensive income (loss), net of tax, the actuarial gains/losses and prior service costs/credits that arise but were not previously required to be recognized as components of net periodic benefit cost. Other comprehensive income (loss) is adjusted as these amounts are later recognized in income as components of net periodic benefit cost.
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) AOCI, which is included as a component of stockholders’ equity, includes unrealized gains or losses on derivative instruments, currency translation adjustments in foreign subsidiaries and minimum pension liability adjustments.
Income Taxes	Income Taxes Deferred income taxes are determined based on the estimated future tax effects of differences between financial statement carrying amounts and the tax bases of existing assets and liabilities. Deferred tax assets are recognized to the extent that realization of those assets is considered to be more likely than not. A valuation allowance is established for deferred taxes when it is more likely than not that all or a portion of the deferred tax assets will not be realized. Provisions are made for the U.S. income tax liability and additional non-U.S. taxes on the undistributed earnings of non-U.S. subsidiaries, except for amounts Cabot has designated to be indefinitely reinvested. Cabot records benefits for uncertain tax positions based on an assessment of whether the position is more likely than not to be sustained by the taxing authorities. If this threshold is not met, no tax benefit of the uncertain tax position is recognized. If the threshold is met, the tax benefit that is recognized is the largest amount that is greater than 50% likely of being realized upon ultimate settlement. This analysis presumes the taxing authorities’ full knowledge of the positions taken and all relevant facts, but does not consider the time value of money. The Company also accrues for interest and penalties on its uncertain tax positions and includes such charges in its income tax provision in the Consolidated Statements of Operations.
Environmental Costs	Environmental Costs Cabot accrues environmental costs when it is probable that a liability has been incurred and the amount can be reasonably estimated. When a single liability amount cannot be reasonably estimated, but a range can be reasonably estimated, Cabot accrues the amount that reflects the best estimate within that range or the low end of the range if no estimate within the range is better. The amount accrued reflects Cabot’s assumptions about remediation requirements at the contaminated site, the nature of the remedy, the outcome of discussions with regulatory agencies and other potentially responsible parties at multi-party sites, and the number and financial viability of other potentially responsible parties. Cabot does not reduce its estimated liability for possible recoveries from insurance carriers. Proceeds from insurance carriers are recorded when realized by either the receipt of cash or a contractual agreement.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make certain estimates and assumptions that affect the reported amount of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reported period. Actual results could differ from those estimates.
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards In February 2016, the FASB issued a new standard for the accounting for leases. This standard requires lessees to recognize assets and liabilities for most leases, including operating leases that were previously not recorded on the balance sheet, and recognize expenses on their income statements in a manner that is similar to the historical accounting treatment for leases. The Company adopted the standard on October 1, 2019 using the modified retrospective optional transition method. Accordingly, leases in the prior period continue to be reported and disclosed in accordance with the Company’s historical accounting treatment. The Company elected the package of practical expedients that permits the Company to not reassess the identification, classification and initial direct costs of leases commencing before the October 1, 2019 effective date and to exclude short-term leases from the balance sheet. The Company did not elect the hindsight practical expedient to determine the lease term for existing leases or the practical expedient to not separate lease and non-lease components to existing leases, as well as new leases, through transition. The Company allocates the total consideration to the lease components and non-lease components on an observable stand-alone price basis to all asset classes. Adoption of the new lease standard resulted in the recognition of operating lease right-of-use (“ROU”) assets and operating lease liabilities of $106 million and $111 million, respectively, as of October 1, 2019. Refer to Note T for further details regarding the balance sheet classification of these items. The difference between the operating lease ROU assets and operating lease liabilities reflects the reclassification of historical deferred rent balances of $5 million. The effects of transition to the new standard resulted in no cumulative adjustment to retained earnings in the period of adoption. The standard did not materially impact the Company’s Consolidated Statement of Operations or Consolidated Statement of Cash Flows. The new standard did not have a material impact on the Company’s liquidity or debt-covenant compliance as of adoption. In February 2018, the FASB issued a new standard that allows entities to reclassify AOCI to Retained earnings stranded tax effects resulting from changes made as a result of the Tax Cuts and Jobs Act of 2017 (the “Act”). The Company adopted this standard on October 1, 2019 which resulted in the reclassification of a $2 million net gain from AOCI to Retained earnings. The reclassification was primarily related to the Company’s pension plans and derivative instruments.
Recently Issued Accounting Pronouncements	Recently Issued Accounting Pronouncements In June 2016, the FASB issued a new standard on measurement of credit losses. The standard introduces a new "expected loss" impairment model that applies to most financial assets measured at amortized cost and certain other instruments, including trade and other receivables and other financial assets. Entities are required to estimate expected credit losses over the life of financial assets and record an allowance against the assets’ amortized cost basis to present them at the amount expected to be collected. The new standard is effective for fiscal years beginning after December 15, 2019 and early adoption is permitted. The Company adopted this standard on October 1, 2020. The adoption of this standard did not materially impact the Company’s consolidated financial statements. 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.

Acquisitions (Tables)

Acquisitions (Tables)	12 Months Ended
	Sep. 30, 2020
Business Combinations [Abstract]
Schedule of Allocation of Purchase Price Based on Estimates of Fair Value of Assets Acquired and Liabilities Assumed	The final allocation of the purchase price set forth below was based on estimates of the fair value of assets acquired and liabilities assumed as of April 1, 2020. (In millions) Assets Cash $ 1 Accounts Receivable 8 Inventories 4 Prepaid expenses and other current assets 2 Property, plant and equipment 38 Intangible assets 15 Goodwill 45 Deferred tax asset 1 Other assets 2 Total assets acquired 116 Liabilities Accounts payable and accrued liabilities (12 ) Long-term debt (13 ) Other liabilities (6 ) Total liabilities assumed (31 ) Cash consideration paid $ 85

Inventories (Tables)

Inventories (Tables)	12 Months Ended
	Sep. 30, 2020
Inventory Disclosure [Abstract]
Components of Company's Inventories	Inventories, net of obsolete, unmarketable and slow moving reserves, are as follows: September 30 2020 2019 (In millions) Raw materials $ 82 $ 107 Finished goods 225 305 Other (1) 52 54 Total $ 359 $ 466 (1) Other inventory is comprised of certain spare parts and supplies.

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Components of Property, Plant and Equipment	Property, plant and equipment consists of the following: September 30 2020 2019 (In millions) Land and land improvements $ 111 $ 144 Buildings 552 524 Machinery and equipment 2,589 2,369 Other 244 247 Construction in progress 190 262 Total property, plant and equipment 3,686 3,546 Less: Accumulated depreciation (2,372 ) (2,198 ) Net property, plant and equipment $ 1,314 $ 1,348

Purification Solutions Goodwi_2

Purification Solutions Goodwill and Long-Lived Assets Impairment Charges (Tables)	12 Months Ended
	Sep. 30, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Impairment Charges and Associated Deferred Tax Benefit	During the second quarter of fiscal 2018, the Company performed a long-lived asset impairment test and quantitative goodwill impairment test, which determined that the estimated fair value of the Purification Solutions reporting unit was lower than the reporting unit's carrying value. The Company recorded impairment charges relating to the goodwill and long-lived assets of the Purification Solutions reporting unit, and an associated deferred tax benefit, in the Consolidated Statements of Operations as follows: Three Months Ended March 31, 2018 (In millions) Purification Solutions goodwill impairment charge $ 92 Purification Solutions long-lived assets impairment charge 162 Benefit for income taxes (30 ) Impairment charges, after tax $ 224

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Sep. 30, 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 period ended September 30, 2020 are as follows Reinforcement Materials Performance Chemicals Total (2) (In millions) Balance at September 30, 2019 $ 50 $ 40 90 Goodwill acquired (1) — 45 45 Foreign currency impact (4 ) 3 (1 ) Balance at September 30, 2020 $ 46 $ 88 $ 134 (1) (2)
Schedule of Intangible Assets	The following table provides information regarding the Company’s intangible assets: September 30, 2020 September 30, 2019 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 $ 60 $ (8 ) $ 52 $ 50 $ (5 ) $ 45 Trademarks 11 (1 ) 10 8 — 8 Customer relationships 56 (15 ) 41 57 (14 ) 43 Total intangible assets (1) $ 127 $ (24 ) $ 103 $ 115 $ (19 ) $ 96 (1) Total intangible assets as of September 30, 2020 includes $15 million of intangible assets from the acquisition of SUSN as described in Note C.

Accounts Payable, Accrued Lia_2

Accounts Payable, Accrued Liabilities and Other Liabilities (Tables)	12 Months Ended
	Sep. 30, 2020
Payables And Accruals [Abstract]
Components of Accounts Payable and Accrued Liabilities	Accounts payable and accrued liabilities included in current liabilities consist of the following: September 30 2020 2019 (In millions) Accounts payable $ 316 $ 390 Accrued employee compensation 46 51 Accrued legal expenses (1) 38 6 Other accrued liabilities 88 90 Total $ 488 $ 537 (1)
Components of Other Long-Term Liabilities	Other long-term liabilities consist of the following: September 30 2020 2019 (In millions) Employee benefit plan liabilities $ 92 $ 91 Operating lease liabilities 89 — Non-current tax liabilities 9 12 Other accrued liabilities 96 103 Total $ 286 $ 206

Debt and Other Obligations (Tab

Debt and Other Obligations (Tables)	12 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Schedule of Long-Term Obligations	The Company’s long-term obligations, the fiscal year in which they mature and their respective interest rates are summarized below: September 30 2020 2019 (In millions) Variable Rate Debt: Revolving Credit Facility, expires fiscal 2023 $ — $ — Revolving Credit Facility - Canada, expires fiscal 2021 — 43 Revolving Credit Facility - Euro, expires fiscal 2024 148 56 Total variable rate debt 148 99 Fixed Rate Debt: 3.7% Notes due fiscal 2022 350 350 3.4% Notes due fiscal 2026 250 250 4.0% Notes due fiscal 2029 300 300 Medium Term Notes: Notes due fiscal 2022, 8.34% — 8.47% 15 15 Notes due fiscal 2028, 6.57% — 7.28% 8 8 Total Medium Term Notes 23 23 Chinese Renminbi Debt, due fiscal 2020, 4.35% — 4 Chinese Renminbi Debt, due fiscal 2021, 4.35% 4 — Total fixed rate debt 927 927 Finance lease obligations (Note T) 31 12 Unamortized debt issuance costs and debt discount (5 ) (7 ) Total debt 1,101 1,031 Less current portion of long-term debt (7 ) (7 ) Total long-term debt $ 1,094 $ 1,024
Schedule of Future Years Payment	The aggregate principal amounts of long-term debt, excluding finance lease liabilities presented separately in Note T, due in each of the five years from fiscal 2021 through 2025 and thereafter are as follows: Years Ending September 30 Principal Payments on Long-Term Debt (In millions) 2021 $ 4 2022 365 2023 — 2024 148 2025 — Thereafter 558 Total $ 1,075

Derivatives (Tables)

Derivatives (Tables)	12 Months Ended
	Sep. 30, 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 September 30, 2020 and 2019 to manage foreign currency risk. Notional Amount Description Borrowing September 30, 2020 September 30, 2019 Hedge Designation Cross Currency Swaps 3.4% Notes USD 250 million swapped to EUR 223 million USD 250 million swapped to EUR 223 million Net investment Forward Foreign Currency Contracts (1) N/A USD 54 million USD 54 million No designation (1) As of September 30, 2020, Cabot’s forward foreign exchange contracts were denominated in Canadian dollar, Indonesian rupiah and Czech koruna. As of September 30, 2019, Cabot’s forward foreign exchange contracts were denominated in British pound, Canadian dollar, Indonesian rupiah and Czech koruna.
Summary Impact of Cross-currency Swaps to AOCI and Consolidated Statements of Operations	The following table summarizes the impact of the cross-currency swaps to AOCI and the Consolidated Statements of Operations: Years Ended September 30 2020 2019 2018 2020 2019 2018 2020 2019 2018 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 $ 1 $ 23 $ (2 ) $ (5 ) $ (5 ) $ (5 ) $ 2 $ 1 $ 2

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Sep. 30, 2020
Compensation And Retirement Disclosure [Abstract]
Change in Benefit Obligations and Change in Plan Assets	The following provides information about projected benefit obligations, plan assets, the funded status and weighted-average assumptions of the defined benefit pension and postretirement benefit plans: Years Ended September 30 2020 2019 2020 2019 Pension Benefits Postretirement Benefits U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign (In millions) Change in Benefit Obligations: Benefit obligation at beginning of year $ 157 $ 220 $ 143 $ 373 $ 28 $ 20 $ 29 $ 19 Service cost 1 5 1 7 — — — — Interest cost 4 3 5 5 1 — 1 1 Plan participants’ contribution — 1 — 1 — — — — Foreign currency exchange rate changes — 7 — (13 ) — — — (1 ) Loss from changes in actuarial assumptions and plan experience 2 5 21 — 1 — 1 2 Benefits paid (7 ) (8 ) (11 ) (7 ) (3 ) — (3 ) (1 ) Settlements or curtailments (57 ) (2 ) (1 ) (134 ) — — — — Divestiture of Specialty Fluids — — — (13 ) — — — — Other (1 ) — (1 ) 1 — — — — Benefit obligation at end of year $ 99 $ 231 $ 157 $ 220 $ 27 $ 20 $ 28 $ 20 Years Ended September 30 2020 2019 2020 2019 Pension Benefits Postretirement Benefits U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign (In millions) Change in Plan Assets: Fair value of plan assets at beginning of year $ 151 $ 195 $ 149 $ 323 $ — $ — $ — $ — Actual return on plan assets 9 7 14 17 — — — — Employer contribution 1 6 1 7 3 — 3 1 Plan participants’ contribution — 1 — 1 — — — — Foreign currency exchange rate changes — 5 — (11 ) — — — — Benefits paid (7 ) (8 ) (11 ) (7 ) (3 ) — (3 ) (1 ) Settlements (57 ) (2 ) (1 ) (124 ) — — — — Divestiture — — — (10 ) — — — — Expenses paid from assets (1 ) — (1 ) (1 ) — — — — Fair value of plan assets at end of year $ 96 $ 204 $ 151 $ 195 $ — $ — $ — $ — Funded status $ (3 ) $ (27 ) $ (6 ) $ (25 ) $ (27 ) $ (20 ) $ (28 ) $ (20 ) Recognized asset (liability) $ (3 ) $ (27 ) $ (6 ) $ (25 ) $ (27 ) $ (20 ) $ (28 ) $ (20 )
Assumptions Used to Determine Pension Benefit Obligations and Periodic Benefit Costs, Postretirement Benefit Obligations and Net Costs	Pension Assumptions and Strategy The following assumptions were used to determine the pension benefit obligations and periodic benefit costs as of and for the years ended September 30: 2020 2019 2018 Pension Benefits U.S. Foreign U.S. Foreign U.S. Foreign Actuarial assumptions as of the year-end measurement date: Discount rate 3.1 % 1.7 % 2.6 % 1.8 % 4.2 % 2.4 % Rate of increase in compensation N/A 3.0 % N/A 3.0 % N/A 2.7 % Cash balance interest credit rate 0.9 % 1.7 % 0.9 % 1.9 % 3.3 % 2.0 % Actuarial assumptions used to determine net periodic benefit cost during the year: Discount rate - benefit obligation 2.6 % 1.8 % 4.2 % 2.4 % 3.6 % 2.4 % Discount rate - service cost N/A 1.8 % N/A 2.5 % N/A 2.4 % Discount rate - interest cost 2.6 % 1.6 % 3.9 % 2.1 % 3.0 % 2.0 % Expected long-term rate of return on plan assets 2.5 % 5.2 % 6.3 % 4.9 % 6.8 % 4.9 % Rate of increase in compensation N/A 3.0 % N/A 2.7 % N/A 2.7 % Cash balance interest credit rate 0.9 % 1.9 % 3.3 % 2.0 % 3.3 % 2.0 % Postretirement Assumptions and Strategy The following assumptions were used to determine the postretirement benefit obligations and net costs as of and for the years ended September 30: 2020 2019 2018 Postretirement Benefits U.S. Foreign U.S. Foreign U.S. Foreign Actuarial assumptions as of the year-end measurement date: Discount rate 2.1 % 2.4 % 2.9 % 2.4 % 4.1 % 3.2 % Initial health care cost trend rate 6.0 % 6.9 % 6.5 % 6.9 % 7.0 % 7.0 % Actuarial assumptions used to determine net cost during the year: Discount rate - benefit obligation 2.9 % 2.4 % 4.1 % 3.2 % 3.4 % 3.1 % Discount rate - service cost 2.6 % 2.9 % 4.0 % 3.5 % 3.1 % 3.6 % Discount rate - interest cost 2.5 % 2.3 % 3.7 % 3.1 % 2.8 % 3.0 % Initial health care cost trend rate 6.5 % 6.9 % 7.0 % 7.0 % 7.0 % 7.1 %
Amounts Recognized in Consolidated Balance Sheets	Amounts recognized in the Consolidated Balance Sheets at September 30, 2020 and 2019 related to the Company's defined benefit pension and postretirement benefit plans were as follows: September 30 2020 2019 2020 2019 Pension Benefits Postretirement Benefits U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign (In millions) Other assets $ — $ 21 $ — $ 19 $ — $ — $ — $ — Accounts payable and accrued liabilities $ — $ (2 ) $ (3 ) $ (1 ) $ (3 ) $ (1 ) $ (3 ) $ — Other liabilities $ (3 ) $ (46 ) $ (3 ) $ (43 ) $ (24 ) $ (19 ) $ (25 ) $ (20 )
Amounts Recognized in AOCI	Amounts recognized in AOCI at September 30, 2020 and 2019 related to the Company's defined benefit pension and postretirement benefit plans were as follows: September 30 2020 2019 2020 2019 Pension Benefits Postretirement Benefits U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign (In millions) Net actuarial (gain) loss $ 6 $ 40 $ 13 $ 36 $ (4 ) $ 4 $ (6 ) $ 6 Net prior service credit — — — — — — — — Balance in accumulated other comprehensive income (loss), pretax $ 6 $ 40 $ 13 $ 36 $ (4 ) $ 4 $ (6 ) $ 6
Estimated Future Benefit Payments	Estimated Future Benefit Payments The Company expects that the following benefit payments will be made to plan participants in the years from 2021 to 2030: Pension Benefits Postretirement Benefits Years Ending September 30 U.S. Foreign U.S. Foreign (In millions) 2021 $ 96 $ 12 $ 3 $ 1 2022 $ — $ 10 $ 3 $ 1 2023 $ — $ 10 $ 3 $ 1 2024 $ — $ 12 $ 2 $ 1 2025 $ — $ 11 $ 2 $ 1 2026 - 2030 $ 1 $ 57 $ 9 $ 4 (1)
Net Periodic Defined Benefit Pension and Other Postretirement Benefit Costs	Net periodic defined benefit pension and other postretirement benefit costs include the following components: Years Ended September 30 2020 2019 2018 2020 2019 2018 Pension Benefits Postretirement Benefits U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign (In millions) Service cost $ 1 $ 5 $ 1 $ 7 $ 1 $ 9 $ — $ — $ — $ — $ — $ — Interest cost 4 3 5 5 5 7 1 — 1 1 1 1 Expected return on plan assets (3 ) (9 ) (9 ) (10 ) (10 ) (15 ) — — — — — — Amortization of prior service cost — — — 2 — — — — (2 ) — (3 ) — Net losses — 3 — 2 — 3 (1 ) 1 (1 ) — (1 ) — Settlements or Curtailments cost 3 1 — (7 ) — — — — — — — — Net periodic (benefit) cost $ 5 $ 3 $ (3 ) $ (1 ) $ (4 ) $ 4 $ — $ 1 $ (2 ) $ 1 $ (3 ) $ 1
Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss), Pre-Tax	Other changes in plan assets and benefit obligations recognized in Other comprehensive income (loss) are as follows: Years Ended September 30 2020 2019 2018 2020 2019 2018 Pension Benefits Postretirement Benefits U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign U.S. Foreign (In millions) Net (gains) losses $ (4 ) $ 8 $ 14 $ (16 ) $ (4 ) $ — $ 1 $ (1 ) $ — $ 2 $ (2 ) $ (1 ) Prior service (credit) cost — — — 3 — — — — — — — — Amortization of prior service credit — — — (2 ) — — — — 2 — 3 — Amortization of prior unrecognized loss — (3 ) — (2 ) — (3 ) 1 (1 ) 1 — 1 — Loss on divestiture — — — (2 ) — — — — — — — — (Loss) gain on settlements (3 ) (1 ) — 7 — — — — — — — — Other — — — — — — — — — — — — Net changes recognized in Total other comprehensive (income) loss (1) $ (7 ) $ 4 $ 14 $ (12 ) $ (4 ) $ (3 ) $ 2 $ (2 ) $ 3 $ 2 $ 2 $ (1 ) (1)
Defined Benefit Pension Plans Weighted-Average Asset Allocations	The Company’s defined benefit pension plans weighted-average asset allocations at September 30, 2020 and 2019 by asset category, are as follows: September 30 2020 2019 Pension Assets U.S. Foreign U.S. Foreign Equity securities — % 39 % — % 39 % Debt securities 95 % 50 % 68 % 50 % Real estate — % 6 % — % 6 % Cash and other securities 5 % 5 % 32 % 5 % Total 100 % 100 % 100 % 100 %
Fair Value of Pension Plan Assets by Asset Category	The fair value of the Company’s pension plan assets at September 30, 2020 and 2019 by asset category is as follows: September 30 2020 2019 Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Total Quoted Prices in Active Markets for Identical Assets (Level 1) Significant Observable Inputs (Level 2) Total (In millions) Cash $ 4 $ — $ 4 $ 2 $ — $ 2 Direct investments: U.S government bonds 12 — 12 — — — U.S. corporate bonds 84 — 84 — — — Non-U.S. equities 4 — 4 3 — 3 Non-U.S. government bonds 2 — 2 2 — 2 Non-U.S. corporate bonds 3 — 3 3 — 3 Mortgage backed securities — 1 1 — 1 1 Other fixed income 1 — 1 1 — 1 Total direct investments 106 1 107 9 1 10 Investment funds: Equity funds (1) — 76 76 — 74 74 Fixed income funds (2) — 95 95 104 90 194 Real estate funds (3) — 12 12 — 12 12 Cash equivalent funds 1 — 1 48 — 48 Total investment funds 1 183 184 152 176 328 Alternative investments: Insurance contracts (4) — 5 5 — 5 5 Other alternative investments — — — 1 — 1 Total alternative investments — 5 5 1 5 6 Total pension plan assets $ 111 $ 189 $ 300 $ 164 $ 182 $ 346 (1) The equity funds asset class includes funds that invest in U.S. equities as well as equity securities issued by companies incorporated, listed or domiciled in countries in developed and/or emerging markets. These companies may be in the small-, mid- or large-cap categories. (2) The fixed income funds asset class includes investments in high quality funds. High quality fixed income funds primarily invest in low risk U.S. and non-U.S. government securities, investment-grade corporate bonds, mortgages and asset-backed securities. A significant portion of the fixed income funds include investment in long-term bond funds. (3) The real estate funds asset class includes funds that primarily invest in entities which are principally engaged in the ownership, acquisition, development, financing, sale and/or management of income-producing real estate properties, both commercial and residential. These funds typically seek long-term growth of capital and current income that is above average relative to public equity funds. (4) Insurance contracts held by the Company’s non-U.S. plans are issued by well-known, highly rated insurance companies.

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-Based Compensation Expenses	The following table presents stock-based compensation expenses included in the Company’s Consolidated Statements of Operations: Years Ended September 30 2020 2019 2018 (In millions) Cost of sales $ 1 $ 1 $ 2 Selling and administrative expenses 7 9 19 Research and technical expenses 1 1 1 Stock-based compensation expense 9 11 22 Income tax benefit — (3 ) (6 ) Net stock-based compensation expense $ 9 $ 8 $ 16
Equity Incentive Plan Activity	The following table summarizes the total stock option and restricted stock unit activity in the equity incentive plans for fiscal 2020: Stock Options Restricted Stock Units Total Options (4) Weighted Average Exercise Price Weighted Average Grant Date Fair Value Restricted Stock Units (1) Weighted Average Grant Date Fair Value (Shares in thousands) Outstanding at September 30, 2019 1,022 $ 50.57 $ 12.13 765 $ 53.71 Granted 333 $ 50.23 $ 10.68 276 $ 49.36 Performance-based adjustment (2) — $ — $ — (102 ) $ 53.02 Exercised / Vested (29 ) $ 46.76 $ 6.07 (261 ) $ 50.67 Cancelled / Forfeited (53 ) $ 53.60 $ 7.07 (74 ) $ 55.74 Outstanding at September 30, 2020 (3) 1,273 $ 50.45 $ 11.74 604 $ 52.87 Exercisable at September 30, 2020 664 $ 49.59 (1) The number granted represents the number of shares issuable upon vesting of time-based restricted stock units and performance-based restricted stock units, assuming the Company performs at the target performance level in each year of the three-year performance period. (2) Represents the net incremental number of shares cancelled based on the Company’s actual financial performance metrics for fiscal 20 20 . (3) Stock options outstanding include options vested and expected to vest in the future and have a weighted average remaining contractual life of 6.66 (4) Unvested stock options were approximately 609,000 51.38
Weighted-Average Assumptions	The fair values on the grant date were calculated using the following weighted-average assumptions: Years Ended September 30 2020 2019 2018 Expected stock price volatility 28 % 27 % 28 % Risk free interest rate 1.9 % 3.1 % 2.2 % Expected life of options (years) 6 6 6 Expected annual dividends per year $ 1.40 $ 1.32 $ 1.26

Restructuring (Tables)

Restructuring (Tables)	12 Months Ended
	Sep. 30, 2020
Restructuring And Related Activities [Abstract]
Recorded Restructuring Activities	Cabot’s restructuring activities were recorded in the Consolidated Statements of Operations as follows: Years Ended September 30 2020 2019 2018 (In millions) Cost of sales $ 6 $ 9 $ (31 ) Selling and administrative expenses 13 7 1 Total $ 19 $ 16 $ (30 )
Restructuring Activities and Related Reserves	Details of all restructuring activities and the related reserves for fiscal 2018, 2019, and 2020 were as follows: Severance and Employee Benefits Environmental Remediation and Decommissioning Activities Non-Cash Asset Impairment and Accelerated Depreciation Asset Sales Other Total (In millions) Reserve at September 30, 2017 $ 1 $ 2 $ — $ — $ — $ 3 Charges (gain) 2 3 1 (38 ) 2 (30 ) Costs charged against assets — — (1 ) (1 ) — (2 ) Cash (paid) received (2 ) (1 ) — 39 (2 ) 34 Reserve at September 30, 2018 1 4 — — — 5 Charges (gain) 11 — 2 — 3 16 Costs charged against liabilities — — (2 ) — — (2 ) Cash paid (9 ) — — — (3 ) (12 ) Reserve at September 30, 2019 3 4 — — — 7 Charges (gain) 14 — 1 — 4 19 Costs charged against assets — — (1 ) — — (1 ) Cash (paid) received (12 ) — — — (4 ) (16 ) Reserve at September 30, 2020 $ 5 $ 4 $ — $ — $ — $ 9

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Changes in Each Component of AOCI, Net of Tax	Changes in each component of AOCI, net of tax, are as follows for fiscal 2019 and 2020: Currency Translation Adjustment Unrealized Gains on Investment Pension and Other Postretirement Benefit Liability Adjustment Total (In millions) Balance at September 30, 2018 attributable to Cabot Corporation $ (266 ) $ 1 $ (52 ) $ (317 ) Other comprehensive income (loss) before reclassifications (69 ) — 4 (65 ) Amounts reclassified from AOCI (9 ) — (6 ) (15 ) Less: Other comprehensive income (loss) attributable to noncontrolling interests (6 ) — — (6 ) Balance at September 30, 2019 attributable to Cabot Corporation (338 ) 1 (54 ) (391 ) Other comprehensive income (loss) before reclassifications 42 — 3 45 Amounts reclassified from AOCI (3 ) — 6 3 Adoption of accounting standards (3 ) (1 ) 1 (3 ) Less: Other comprehensive income (loss) attributable to noncontrolling interests 5 — — 5 Balance at September 30, 2020 attributable to Cabot Corporation $ (307 ) $ — $ (44 ) $ (351 )
Amounts Reclassified Out of AOCI	The amounts reclassified out of AOCI and into the Consolidated Statements of Operations for fiscal 2020, 2019 and 2018 are as follows: Affected Line Item in the Consolidated Years Ended September 30 Statements of Operations 2020 2019 2018 (In Millions) Derivatives: net investment hedges (Gains) losses reclassified to interest expense Interest expense $ (5 ) $ (5 ) $ (5 ) (Gains) losses excluded from effectiveness testing and amortized to interest expense Interest expense 2 1 2 Pension and other postretirement benefit liability adjustment Amortization of actuarial losses and prior service cost (credit) Net Periodic Benefit Cost - see Note N for details 3 1 (1 ) Settlement and curtailment loss (gain) Net Periodic Benefit Cost - see Note N for details 4 (7 ) — Specialty Fluids divestiture Specialty Fluids loss on sale and asset impairment - see Note D for details — (3 ) — Total before tax 4 (13 ) (4 ) Tax impact Provision (benefit) for income taxes (1 ) (2 ) 1 Total after tax $ 3 $ (15 ) $ (3 )

Earnings Per Share (Tables)

Earnings Per Share (Tables)	12 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Components of Basic and Diluted Earnings Per Common Share (EPS)	The following tables summarize the components of the basic and diluted earnings per common share (“EPS”) computations: Years Ended September 30 2020 2019 2018 (In millions, except per share amounts) Basic EPS: Net income (loss) attributable to Cabot Corporation $ (238 ) $ 157 $ (113 ) Less: Dividends and dividend equivalents to participating securities — 1 1 Less: Undistributed earnings allocated to participating securities (1) — 1 — Earnings (loss) allocated to common shareholders (numerator) $ (238 ) $ 155 $ (114 ) Weighted average common shares and participating securities outstanding 57.3 59.5 62.4 Less: Participating securities (1) 0.7 0.8 0.7 Adjusted weighted average common shares (denominator) 56.6 58.7 61.7 Per share amounts—basic: Net income (loss) attributable to Cabot Corporation $ (4.21 ) $ 2.64 $ (1.85 ) Diluted EPS: Earnings (loss) allocated to common shareholders $ (238 ) $ 155 $ (114 ) Plus: Earnings allocated to participating securities — 2 — Less: Adjusted earnings allocated to participating securities (2) — 2 — Earnings (loss) available to common shares (numerator) $ (238 ) $ 155 $ (114 ) Adjusted weighted average common shares outstanding 56.6 58.7 61.7 Effect of dilutive securities: Common shares issuable (3) — 0.1 — Adjusted weighted average common shares (denominator) 56.6 58.8 61.7 Per share amounts—diluted: Net income (loss) attributable to Cabot Corporation $ (4.21 ) $ 2.63 $ (1.85 ) (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: Years Ended September 30 2020 2019 2018 (In millions) Calculation of undistributed earnings: Net income (loss) attributable to Cabot Corporation $ (238 ) $ 157 $ (113 ) Less: Dividends declared on common stock 80 80 79 Less: Dividends and dividend equivalents to participating securities — 1 1 Undistributed earnings (loss) $ (318 ) $ 76 $ (193 ) Allocation of undistributed earnings: Undistributed earnings (loss) allocated to common shareholders $ (318 ) $ 75 $ (193 ) Undistributed earnings allocated to participating securities — 1 — Undistributed earnings (loss) $ (318 ) $ 76 $ (193 ) (2) (3)

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Income Before Income Taxes	Income from continuing operations before income taxes and equity in net earnings of affiliated companies was as follows: Years Ended September 30 2020 2019 2018 (In millions) Domestic $ (274 ) $ (66 ) $ (229 ) Foreign 241 321 346 Income from continuing operations before income taxes and equity in earnings of affiliated companies $ (33 ) $ 255 $ 117
Provision (Benefit) for Income Taxes	Tax provision (benefit) for income taxes consisted of the following: Years Ended September 30 2020 2019 2018 (In millions) U.S. federal and state: Current $ (1 ) $ 2 $ 14 Deferred 139 (30 ) 114 Total 138 (28 ) 128 Foreign: Current 62 95 88 Deferred (9 ) 3 (23 ) Total 53 98 65 Provision (benefit) for income taxes $ 191 $ 70 $ 193
Reconciliation Using U.S. Statutory Rate	The provision ( benefit Years Ended September 30 2020 2019 2018 (In millions) Computed tax expense at the federal statutory rate $ (7 ) $ 53 $ 29 Foreign impact of taxation at different rates, repatriation, valuation allowance, and other 4 17 (8 ) Impact of the Tax Cuts and Jobs Act of 2017 — — 159 Global Intangible Low Taxed Income (GILTI) (4 ) 10 — Impact of the Coronavirus Aid, Relief, and Economic Security ("CARES") Act of 2020 (10 ) — — Impact of increase (decrease) in valuation allowance on U.S. deferred taxes 228 — — U.S. and state benefits from research and experimentation activities (2 ) (2 ) (2 ) Provision (settlement) of unrecognized tax benefits (7 ) (8 ) 1 Impact of goodwill impairment charge — — 18 Permanent differences, net — 1 (1 ) State taxes, net of federal effect (11 ) (1 ) (3 ) Provision (benefit) for income taxes $ 191 $ 70 $ 193
Components of Deferred Income Taxes	Significant components of deferred income taxes were as follows: September 30 2020 2019 (In millions) Deferred tax assets: Deferred expenses $ 19 $ 15 Intangible assets 37 28 Inventory 13 9 Operating lease liability 20 — Other 32 3 Pension and other benefits 35 41 Net operating loss carryforwards 109 124 Foreign tax credit carryforwards 58 20 R&D credit carryforwards 44 43 Other business credit carryforwards 23 29 Subtotal 390 312 Valuation allowance (317 ) (124 ) Total deferred tax assets $ 73 $ 188 September 30 2020 2019 (In millions) Deferred tax liabilities: Property, plant and equipment $ (40 ) $ (61 ) Right of use asset (20 ) - Unremitted earnings of non-U.S. subsidiaries (18 ) (5 ) Total deferred tax liabilities $ (78 ) $ (66 )
Expiration Dates of NOLs and Other Tax Credit Carryforwards Before Valuation Allowances	The following table provides detail surrounding the expiration dates of NOLs and other tax credit carryforwards before valuation allowances: Years Ending September 30 NOLs Credits (In millions) 2021 - 2027 $ 168 $ 50 2028 and thereafter 198 73 Indefinite carryforwards 287 2 Total $ 653 $ 125
Reconciliation of Unrecognized Tax Benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits for fiscal 2020, 2019 and 2018 is as follows: Years Ended September 30 2020 2019 2018 (In millions) Balance at beginning of the year $ 27 $ 37 $ 36 Additions based on tax provisions related to the current year 2 — 2 Additions for tax positions of prior years 2 — 1 Reductions of tax provisions of prior years (1 ) (1 ) — Reductions related to settlements (5 ) (5 ) — Reductions from lapse of statute of limitations (2 ) (4 ) (2 ) Balance at end of the year $ 23 $ 27 $ 37

Leases (Tables)

Leases (Tables)	12 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Components of Company's Lease Costs	The components of the Company’s lease costs were as follows: Year Ended September 30 2020 (In millions) Operating lease cost $ 32 Finance lease cost 6 Total lease cost $ 38
Supplemental Cash Flow Information Related to Company's Leases	Supplemental cash flow information related to the Company’s leases was as follows: Year Ended September 30 2020 (In millions) Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 25 Operating cash flows from finance leases 2 Financing cash flows from finance leases 3 Right-of-use assets obtained in exchange for new operating lease liabilities $ 14 Right-of-use assets obtained in exchange for new finance lease liabilities $ 24
Supplemental Balance Sheet Information Related to Company's Leases	Supplemental balance sheet information related to the Company’s leases was as follows: Description Balance Sheet Classification September 30, 2020 (In millions) Lease ROU assets: Operating Other assets $ 98 Finance Net property, plant and equipment 44 Total lease ROU assets $ 142 Lease liabilities: Current: Operating Accounts payable and accrued liabilities $ 15 Finance Current portion of long-term debt 3 Long-term: Operating Other liabilities 89 Finance Long-term debt 28 Total lease liabilities $ 135
Weighed Average Remaining Lease Term and Discount Rates	The following table presents the weighted-average remaining lease term and discount rates for the Company’s leases as of September 30, 2020: Description September 30, 2020 Weighted-average remaining lease term (years): Operating leases 17 Finance leases 12 Weighted-average discount rate: Operating leases 2.19 % Finance leases 4.42 %
Future Minimum Lease Payments Under Non-cancelable Operating and Finance Leases	Future minimum lease payments under non-cancelable operating and finance leases as of September 30, 2020 were as follows: Years Ended September 30 Operating leases Finance leases (In millions) 2021 $ 17 $ 5 2022 12 4 2023 11 4 2024 10 4 2025 9 4 2026 and thereafter 67 19 Total lease payments 126 40 Less: imputed interest 22 9 Total $ 104 $ 31 The Company’s future minimum lease payments under non-cancelable leases as of September 30, 2019 were as follows: Years Ended September 30 Operating leases Capital leases (In millions) 2020 $ 23 $ 3 2021 14 3 2022 9 3 2023 9 3 2024 8 2 2025 and thereafter 68 7 Total lease payments 131 21 Less: imputed interest — 9 Total $ 131 $ 12

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Sep. 30, 2020
Commitments And Contingencies Disclosure [Abstract]
Schedule of Raw Material Purchased under Long Term Purchase Agreements	Cabot has entered into long-term purchase agreements primarily for the purchase of raw materials. Under certain of these agreements, the quantity of material being purchased is fixed, but the price paid changes as market prices change. Raw materials purchased under these agreements by segment for fiscal 2020, 2019 and 2018 are as follows: Years Ended September 30 2020 2019 2018 (In millions) Reinforcement Materials $ 198 $ 393 $ 375 Performance Chemicals 58 65 55 Purification Solutions 2 8 11 Total $ 258 $ 466 $ 441
Schedule of Components of Purchase Commitments	For these purchase commitments, the amounts included in the table below are based on market prices as of September 30, 2020 which may differ from actual market prices at the time of purchase. Payments Due by Fiscal Year 2021 2022 2023 2024 2025 Thereafter Total (In millions) Reinforcement Materials $ 115 $ 101 $ 87 $ 86 $ 86 $ 911 $ 1,386 Performance Chemicals 54 53 34 34 35 332 $ 542 Total $ 169 $ 154 $ 121 $ 120 $ 121 $ 1,243 $ 1,928

Financial Information by Segm_2

Financial Information by Segment & Geographic Area (Tables)	12 Months Ended
	Sep. 30, 2020
Segment Reporting [Abstract]
Schedule of Performance Segment	The net sales from each of these businesses for fiscal 2020, 2019 and 2018 are as follows: Years Ended September 30 2020 2019 2018 (In millions) Performance Additives $ 645 $ 694 $ 707 Formulated Solutions 288 301 321 Total Performance Chemicals $ 933 $ 995 $ 1,028
Financial Information by Reportable Segment	Financial information by reportable segment is as follows: Years Ended September 30 Reinforcement Materials Performance Chemicals Purification Solutions Specialty Fluids Segment Total (1) Unallocated and Other (2), (4) Consolidated Total (In millions) 2020 Revenues from external customers (3) $ 1,256 $ 933 $ 253 $ — $ 2,442 $ 172 $ 2,614 Depreciation and amortization $ 68 $ 64 $ 24 $ — $ 156 $ 2 $ 158 Equity in earnings of affiliated companies $ — $ 1 $ 3 $ — $ 4 $ (1 ) $ 3 Income (loss) from continuing operations before income taxes (4) $ 162 $ 118 $ 3 $ — $ 283 $ (316 ) $ (33 ) Assets (5) $ 1,077 $ 1,145 $ 296 $ — $ 2,518 $ 263 $ 2,781 Total expenditures for additions to long-lived assets (6) $ 66 $ 92 $ 8 $ — $ 166 $ 3 $ 169 2019 Revenues from external customers (3) $ 1,815 $ 995 $ 278 $ 56 $ 3,144 $ 193 $ 3,337 Depreciation and amortization $ 69 $ 51 $ 26 $ 1 $ 147 $ 1 $ 148 Equity in earnings of affiliated companies $ (1 ) $ 1 $ 3 $ — $ 3 $ (2 ) $ 1 Income (loss) from continuing operations before income taxes (4) $ 266 $ 152 $ 2 $ 24 $ 444 $ (189 ) $ 255 Assets (5) $ 1,177 $ 1,024 $ 436 $ — $ 2,637 $ 367 $ 3,004 Total expenditures for additions to long-lived assets (6) $ 82 $ 148 $ 11 $ 1 $ 242 $ 5 $ 247 2018 Revenues from external customers (3) $ 1,774 $ 1,028 $ 279 $ 45 $ 3,126 $ 116 $ 3,242 Depreciation and amortization $ 70 $ 48 $ 32 $ 2 $ 152 $ (3 ) $ 149 Equity in earnings of affiliated companies $ 1 $ — $ 6 $ — $ 7 $ (5 ) $ 2 Income (loss) from continuing operations before income taxes (4) $ 279 $ 200 $ (7 ) $ 8 $ 480 $ (363 ) $ 117 Assets (5) $ 1,319 $ 919 $ 460 $ 178 $ 2,876 $ 368 $ 3,244 Total expenditures for additions to long-lived assets (6) $ 97 $ 94 $ 16 $ 17 $ 224 $ 5 $ 229 (1) Cabot divested its Specialty Fluids business on June 28, 2019. Refer to Note D for the terms of this transaction. (2) Unallocated and Other includes certain items and eliminations necessary to reflect management’s reporting of operating segment results. These items are reflective of the segment reporting presented to the CODM. ( 3 ) Consolidated Total Revenues from external customers reconciles to Net sales and other operating revenues on the Consolidated Statements of Operations. Revenues from external customers that are categorized as Unallocated and Other reflects royalties, external shipping and handling fees, the impact of unearned revenue, the removal of 100 % of the sales of an equity method affiliate and discounting charges for certain Notes receivable. Details are provided in the table below. Years Ended September 30 2020 2019 2018 (In millions) Royalties, the impact of unearned revenue, the removal of 100% discounting charges for certain Notes receivable $ (3 ) $ (13 ) $ 11 Shipping and handling fees 113 130 105 By-product sales (a) 62 76 — Total $ 172 $ 193 $ 116 (a) Revenue from Contracts with Customers ( 4 ) Consolidated Total Income (loss) from continuing operations before income taxes reconciles to Income (loss) from continuing operations before income taxes and equity in earnings of affiliated companies on the Consolidated Statements of Operations. Total Income (loss) from continuing operations before income taxes that are categorized as Unallocated and Other includes: Years Ended September 30 2020 2019 2018 (In millions) Interest expense $ (53 ) $ (59 ) $ (54 ) Certain items: (a) Marshall Mine loss on sale and asset impairment charge (Note D) $ (129 ) $ — $ — Legal and environmental matters and reserves (Note U) (54 ) (21 ) (16 ) Global restructuring activities (Note P) (19 ) (16 ) 30 Employee benefit plan settlement and other charges (Note N) (10 ) 1 — Acquisition and integration-related charges (Note C) (5 ) (6 ) (2 ) Inventory reserve adjustment (2 ) — (13 ) Specialty Fluids loss on sale and asset impairment charge (Note D) (1 ) (29 ) — Equity affiliate investment impairment charge (Note M) — (11 ) — Executive transition costs — (1 ) (2 ) Indirect tax settlement credits 3 — — Purification Solutions goodwill and long-lived assets impairment charge (Note G) — — (254 ) Gains (losses) on sale of investments — — 10 Other certain items (1 ) (4 ) (1 ) Total certain items, pre-tax (218 ) (87 ) (248 ) Unallocated corporate costs (b) (41 ) (50 ) (61 ) General unallocated income (expense) (c) (1 ) 8 2 Less: Equity in earnings of affiliated companies, net of tax (d) 3 1 2 Total $ (316 ) $ (189 ) $ (363 ) (a) Certain items are items that management does not consider representative of operating segment results and they are, therefore, excluded from Segment EBIT. (b) Unallocated corporate costs are not controlled by the segments and primarily benefit corporate interests. (c) General unallocated income (expense) consists of gains (losses) arising from foreign currency transactions, net of other foreign currency risk management activities, interest income, dividend income, the profit or loss related to the corporate adjustment for unearned revenue, and the impact of including the full operating results of a contractual joint venture in Purification Solutions Segment EBIT. (d) Equity in earnings of affiliated companies, net of tax is included in Segment EBIT and is removed from Unallocated and other to reconcile to income (loss) from operations before taxes. ( 5 ) Unallocated and Other assets includes cash, marketable securities, cost investments, income taxes receivable, deferred taxes, headquarters’ assets, and current and non-current assets held for sale. ( 6 ) Expenditures for additions to long-lived assets include total equity and other investments (including available-for-sale securities) and property, plant and equipment.
Revenues from External Customers and Long-Lived Asset Information by Geographic Area	Revenues from external customers attributable to an individual country, other than the U.S. and China, were not material for disclosure. Revenues from external customers by individual country are summarized as follows: Years Ended September 30 2020 2019 2018 (In millions) United States $ 581 $ 702 $ 676 China 598 738 752 Other countries 1,435 1,897 1,814 Total $ 2,614 $ 3,337 $ 3,242 Long-lived assets attributable to an individual country, other than the U.S. and China, were not material for disclosure. Long-lived asset information by individual country is summarized as follows: Years Ended September 30 2020 2019 2018 (In millions) United States $ 493 $ 572 $ 493 China 295 264 270 Other countries 526 512 533 Total $ 1,314 $ 1,348 $ 1,296
Revenues from External Customers by Geographic Region	Each of the Company’s segments operate globally. In addition to presenting Revenue from external customers by reportable segment, the following tables further disaggregate Revenue from external customers by geographic region. Year Ended September 30, 2020 Reinforcement Materials Performance Chemicals Purification Solutions Consolidated Total (In millions) Americas $ 490 $ 266 $ 112 $ 868 Asia Pacific 529 368 34 931 Europe, Middle East and Africa 237 299 107 643 Segment revenues from external customers 1,256 933 253 2,442 Unallocated and other 172 Net sales and other operating revenues $ 2,614 Year Ended September 30, 2019 Reinforcement Materials Performance Chemicals Purification Solutions Specialty Fluids Consolidated Total (In millions) Americas $ 688 $ 294 $ 126 $ 6 $ 1,114 Asia Pacific 769 353 35 1 1,158 Europe, Middle East and Africa 358 348 117 49 872 Segment revenues from external customers 1,815 995 278 56 3,144 Unallocated and other 193 Net sales and other operating revenues $ 3,337

Unaudited Quarterly Financial_2

Unaudited Quarterly Financial Information (Tables)	12 Months Ended
	Sep. 30, 2020
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	Unaudited financial results by quarter for fiscal 2020 and 2019 are summarized below: Quarters Ended Year Ended December 31, March 31, June 30, September 30, September 30, 2019 2020 2020 2020 2020 (In millions, except per share amounts) Net sales and other operating revenues $ 727 $ 710 $ 518 $ 659 $ 2,614 Gross profit $ 141 $ 153 $ 69 $ 137 $ 500 Net income (loss) $ 46 $ 3 $ (5 ) $ (265 ) $ (221 ) Net income (loss) attributable to Cabot Corporation $ 41 $ (1 ) $ (6 ) $ (272 ) $ (238 ) Earnings per common share—basic $ 0.71 $ (0.01 ) $ (0.12 ) $ (4.81 ) $ (4.21 ) Earnings per common share—diluted $ 0.70 $ (0.01 ) $ (0.12 ) $ (4.81 ) $ (4.21 ) Quarters Ended Year Ended December 31, March 31, June 30, September 30, September 30, 2018 2019 2019 2019 2019 (In millions, except per share amounts) Net sales and other operating revenues $ 821 $ 844 $ 845 $ 827 $ 3,337 Gross profit $ 166 $ 178 $ 170 $ 171 $ 685 Net income (loss) $ 77 $ 29 $ 40 $ 40 $ 186 Net income (loss) attributable to Cabot Corporation $ 69 $ 23 $ 32 $ 33 $ 157 Earnings per common share—basic $ 1.14 $ 0.39 $ 0.55 $ 0.56 $ 2.64 Earnings per common share—diluted $ 1.14 $ 0.39 $ 0.55 $ 0.55 $ 2.63

Significant Accounting Polici_3

Significant Accounting Policies - Additional Information (Detail) ¥ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2020CNY (¥)	Sep. 30, 2019CNY (¥)
Significant Accounting Policies [Line Items]
Equity affiliate investments		$ 39,000,000	$ 39,000,000
Capitalized interest		2,000,000	4,000,000	$ 2,000,000
Asset retirement obligation reserve		18,000,000	26,000,000
Charges on sale of notes receivables		2,000,000	3,000,000	3,000,000
Changes in allowance		$ 0	0
Chance of utilizing the associated benefit for valuation allowances, maximum		50.00%
Equity Method Investments [Member]
Significant Accounting Policies [Line Items]
Dividends declared		$ 3,000,000	4,000,000	9,000,000
Minimum [Member]
Significant Accounting Policies [Line Items]
Payment terms		0 days
Minimum [Member] | Buildings [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment		20 years
Minimum [Member] | Machinery and Equipment [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment		10 years
Minimum [Member] | Other Fixed Assets [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment		3 years
Minimum [Member] | Cabot [Member]
Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage		20.00%			20.00%
Maximum [Member]
Significant Accounting Policies [Line Items]
Payment terms		90 days
Maximum [Member] | Buildings [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment		25 years
Maximum [Member] | Machinery and Equipment [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment		25 years
Maximum [Member] | Other Fixed Assets [Member]
Significant Accounting Policies [Line Items]
Useful life of property, plant and equipment		25 years
Maximum [Member] | Cabot [Member]
Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage		50.00%			50.00%
Other Nonoperating Income (Expense) [Member]
Significant Accounting Policies [Line Items]
Foreign currency transaction gain (loss)		$ (6,000,000)		$ (4,000,000)
Other Nonoperating Income (Expense) [Member] | Maximum [Member]
Significant Accounting Policies [Line Items]
Foreign currency transaction gain (loss)			1,000,000
Venezuela [Member] | Carbon Black Affiliate [Member]
Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage	49.00%
Venezuela [Member] | Carbon Black Affiliate [Member] | Other Nonoperating Income (Expense) [Member]
Significant Accounting Policies [Line Items]
Impairment charge	$ 11,000,000
China [Member]
Significant Accounting Policies [Line Items]
Accounts and notes receivable, net		$ 5,000,000	$ 4,000,000		¥ 34	¥ 30

Recent Accounting Pronounceme_2

Recent Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Millions	Oct. 01, 2019	Sep. 30, 2020	Sep. 30, 2019
Significant Accounting Policies [Line Items]
Operating lease right-of-use assets	$ 106	$ 98
Operating lease liability	$ 111	$ 104
Operating Lease, Liability, Statement of Financial Position [Extensible List]	cbt:AccountsPayableAndAccruedLiabilitiesAndOtherLiabilitiesMember	cbt:AccountsPayableAndAccruedLiabilitiesAndOtherLiabilitiesMember
Reclassification of deferred rent balances	$ 5
Cumulative adjustment to retained earnings		$ 989	$ 1,337
Reclassification of net gain from Accumulated other comprehensive income (loss) to retained earnings	2
Cumulative Effect, Period of Adoption, Adjustment [Member] | Revision of Prior Period, Adjustment [Member]
Significant Accounting Policies [Line Items]
Cumulative adjustment to retained earnings	$ 0

Acquisitions - Additional Infor

Acquisitions - Additional Information (Detail) - USD ($) $ in Millions	Apr. 01, 2020	Jun. 30, 2020	Sep. 30, 2018	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Business Acquisition [Line Items]
Businesses acquisition, net of cash acquired					$ 92	$ 3	$ 64
Assumed debt repaid					410	75	$ 251
NSCC Carbon (Jiangsu) Co. Ltd [Member]
Business Acquisition [Line Items]
Acquisition date			Sep. 30, 2018
Business acquisition, purchase price			$ 8
Expected production commencement year			2022
Transition related costs					2	$ 4
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
Business acquisition, revenue				$ 12
Acquisition and integration costs				$ 3	$ 3
Shenzhen Sanshun Nano New Materials Co., Ltd [Member] | Developed Technologies [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets	$ 9
Intangible assets amortization period	10 years
Shenzhen Sanshun Nano New Materials Co., Ltd [Member] | Customer Relationships [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets	$ 4
Intangible assets amortization period	20 years
Shenzhen Sanshun Nano New Materials Co., Ltd [Member] | Trademarks [Member]
Business Acquisition [Line Items]
Finite-lived intangible assets	$ 2
Intangible assets amortization period	10 years

Acquisitions - Schedule of Allo

Acquisitions - Schedule of Allocation of Purchase Price Based on Estimates of Fair Value of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Millions	Sep. 30, 2020	[1]	Apr. 01, 2020	Sep. 30, 2019	[1]
Assets
Cash			$ 1
Accounts Receivable			8
Inventories			4
Prepaid expenses and other current assets			2
Property, plant and equipment			38
Intangible assets			15
Goodwill	$ 134		45	$ 90
Deferred tax asset			1
Other assets			2
Total assets acquired			116
Liabilities
Accounts payable and accrued liabilities			(12)
Long-term debt			(13)
Other liabilities			(6)
Total liabilities assumed			(31)
Cash consideration paid			$ 85
[1]

Divestitures - Additional Infor

Divestitures - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2020	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Specialty Fluids [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Impairment charge					$ 1	$ 29
Marshall Mine [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Impairment charge		$ 129			$ 129
Sinomine (Hong Kong) Rare Metals Resources Co. Limited [Member] | Specialty Fluids [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Pre-tax loss on sale			$ 1			$ 9
Impairment charge				$ 20
ADA Carbon Solutions, LLC [Member] | Marshall Mine [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Pre-tax loss on sale		67
Impairment charge		$ 62
Closure costs	$ 9
Closure costs payment period					5 years

Inventories - Components of Com

Inventories - Components of Company's Inventories (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Inventory Disclosure [Abstract]
Raw materials	$ 82	$ 107
Finished goods	225	305
Other	52	54
Total	$ 359	$ 466

Inventories - Additional Inform

Inventories - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Inventory Disclosure [Abstract]
Obsolete inventory reserve	$ 28	$ 29

Property, Plant and Equipment -

Property, Plant and Equipment - Components of Property, Plant and Equipment (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Property Plant And Equipment [Abstract]
Land and land improvements	$ 111	$ 144
Buildings	552	524
Machinery and equipment	2,589	2,369
Other	244	247
Construction in progress	190	262
Total property, plant and equipment	3,686	3,546
Less: Accumulated depreciation	(2,372)	(2,198)
Net property, plant and equipment	$ 1,314	$ 1,348	$ 1,296

Property, Plant and Equipment_2

Property, Plant and Equipment - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Property Plant And Equipment [Abstract]
Depreciation expense	$ 151	$ 142	$ 142

Purification Solutions Goodwi_3

Purification Solutions Goodwill and Long-Lived Assets Impairment Charges - Impairment Charges and Associated Tax Benefit (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Goodwill And Intangible Assets [Line Items]
Purification Solutions goodwill impairment charge				$ 92
Purification Solutions long-lived assets impairment charge				162
Benefit for income taxes		$ 130	$ (27)	$ 91
Purification Solutions [Member]
Goodwill And Intangible Assets [Line Items]
Purification Solutions goodwill impairment charge	$ 92
Purification Solutions long-lived assets impairment charge	162
Benefit for income taxes	(30)
Impairment charges, after tax	$ 224

Purification Solutions Goodwi_4

Purification Solutions Goodwill and Long-Lived Assets Impairment Charges - Additional Information (Detail) $ in Millions	Mar. 31, 2018USD ($)
Purification Solutions [Member]
Goodwill And Intangible Assets [Line Items]
Lower of cost or market reserve inventory	$ 13

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Schedule of Goodwill Balances (Detail) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)
Goodwill And Intangible Assets [Line Items]
Beginning balance	$ 90	[1]
Goodwill acquired	45	[1],[2]
Foreign currency impact	(1)	[1]
Ending balance	134	[1]
Reinforcement Materials [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	50
Foreign currency impact	(4)
Ending balance	46
Performance Chemicals [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	40
Goodwill acquired	45	[2]
Foreign currency impact	3
Ending balance	$ 88
[1]
[2]

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Schedule of Goodwill Balances (Parenthetical) (Detail) - USD ($)	Sep. 30, 2020	Sep. 30, 2019
Purification Solutions [Member]
Goodwill And Intangible Assets [Line Items]
Accumulated impairment losses	$ 444,000,000	$ 444,000,000
Reinforcement Materials [Member]
Goodwill And Intangible Assets [Line Items]
Accumulated impairment losses	0	0
Performance Chemicals [Member]
Goodwill And Intangible Assets [Line Items]
Accumulated impairment losses	$ 0	$ 0

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Schedule of Intangible Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	$ 127	$ 115
Accumulated Amortization	(24)	(19)
Net Intangible Assets, finite lives	103	96
Developed Technologies [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	60	50
Accumulated Amortization	(8)	(5)
Net Intangible Assets, finite lives	52	45
Trademarks [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	11	8
Accumulated Amortization	(1)
Net Intangible Assets, finite lives	10	8
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	56	57
Accumulated Amortization	(15)	(14)
Net Intangible Assets, finite lives	$ 41	$ 43

Goodwill and Intangible Asset_5

Goodwill and Intangible Assets - Schedule of Intangible Assets (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Apr. 01, 2020
Finite Lived Intangible Assets [Line Items]
Intangible assets		$ 15
Shenzhen Sanshun Nano New Materials Co., Ltd [Member]
Finite Lived Intangible Assets [Line Items]
Intangible assets	$ 15

Goodwill and Intangible Asset_6

Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Goodwill And Intangible Assets [Line Items]
Amortization expense estimated for year one	$ 7
Amortization expense estimated for year two	7
Amortization expense estimated for year three	7
Amortization expense estimated for year four	7
Amortization expense estimated for year five	7
Cost of Sales, Selling and Administrative Expenses and Research and Technical Expenses [Member]
Goodwill And Intangible Assets [Line Items]
Amortization of intangible assets	$ 7	$ 6	$ 7
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

Accounts Payable, Accrued Lia_3

Accounts Payable, Accrued Liabilities and Other Liabilities - Components of Accounts Payable and Accrued Liabilities (Detail) - USD ($) $ in Millions		Sep. 30, 2020	Sep. 30, 2019
Payables And Accruals [Abstract]
Accounts payable		$ 316	$ 390
Accrued employee compensation		46	51
Accrued legal expenses	[1]	38	6
Other accrued liabilities		88	90
Total		$ 488	$ 537
[1]

Accounts Payable, Accrued Lia_4

Accounts Payable, Accrued Liabilities and Other Liabilities - Components of Accounts Payable and Accrued Liabilities (Parenthetical) (Detail) $ in Millions	Sep. 30, 2020USD ($)
Payables And Accruals [Abstract]
Accrued liability payable	$ 32.6

Accounts Payable, Accrued Lia_5

Accounts Payable, Accrued Liabilities and Other Liabilities - Components of Other Long-Term Liabilities (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Payables And Accruals [Abstract]
Employee benefit plan liabilities	$ 92	$ 91
Operating lease liabilities	89
Non-current tax liabilities	9	12
Other accrued liabilities	96	103
Total	$ 286	$ 206

Debt and Other Obligations - Sc

Debt and Other Obligations - Schedule of Long-Term Obligations (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Total variable rate debt	$ 148	$ 99
Total Medium Term Notes	23	23
Debt	1,075
Total debt	927	927
Finance lease obligations (Note T)	31	12
Unamortized debt issuance costs and debt discount	(5)	(7)
Total debt	1,101	1,031
Less current portion of long-term debt	(7)	(7)
Total long-term debt	1,094	1,024
Revolving Credit Facility - Canada, expires fiscal 2021 [Member]
Debt Instrument [Line Items]
Line of credit		43
Revolving Credit Facility - Euro, expires fiscal 2024 [Member]
Debt Instrument [Line Items]
Line of credit	148	56
3.7% Notes due fiscal 2022 [Member]
Debt Instrument [Line Items]
Notes	350	350
3.4% Notes due fiscal 2026 [Member]
Debt Instrument [Line Items]
Notes	250	250
Notes due fiscal 2022, 8.34% - 8.47% [Member]
Debt Instrument [Line Items]
Total Medium Term Notes	15	15
Notes due fiscal 2028, 6.57% - 7.28% [Member]
Debt Instrument [Line Items]
Total Medium Term Notes	8	8
4.0% Notes due fiscal 2029 [Member]
Debt Instrument [Line Items]
Notes	300	300
Chinese Renminbi Debt, Due Fiscal 2020, 4.35% [Member]
Debt Instrument [Line Items]
Debt		$ 4
Chinese Renminbi Debt, due fiscal 2021, 4.35% [Member]
Debt Instrument [Line Items]
Debt	$ 4

Debt and Other Obligations - _2

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

Debt and Other Obligations - Ad

Debt and Other Obligations - Additional Information (Detail)	1 Months Ended					3 Months Ended				12 Months Ended
	Jun. 30, 2019USD ($)	Nov. 30, 2018USD ($)	Sep. 30, 2016USD ($)	Nov. 30, 2013USD ($)	Jul. 31, 2012USD ($)	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Jun. 08, 2020	Jun. 07, 2020	May 31, 2019EUR (€)	Sep. 30, 2018USD ($)	Oct. 31, 2015USD ($)
Debt Instrument [Line Items]
Revolving credit facility, committed amount									$ 1,000,000,000	$ 1,000,000,000
Debt instrument, covenant, ratio of consolidated total debt to consolidated EBITDA									4.50	4.50		4.50
Debt instrument, covenant, sum of subsidiary indebtedness and priority indebtedness as percentage of net worth, maximum									10.00%
Debt instrument, covenant, sum of subsidiary indebtedness and priority indebtedness as percentage of net worth, minimum									5.00%
Long-term debt									$ 1,075,000,000	$ 1,075,000,000
Unsecured medium term notes outstanding issued									23,000,000	$ 23,000,000	$ 23,000,000
Maturity of the total outstanding medium term notes, years										4 years
Weighted average interest of medium term notes										7.96%
Short-term borrowings									14,000,000	$ 14,000,000	33,000,000
NHUMO [Member]
Debt Instrument [Line Items]
Preferred stock repurchase amount		$ 25,000,000		$ 25,000,000
Dividend percentage of preferred stock				6.00%
Preferred stock dividend		$ 1,400,000
Commercial Paper [Member]
Debt Instrument [Line Items]
Short-term borrowings									$ 14,000,000	$ 14,000,000	$ 33,000,000
Weighted-average interest rate									0.28%	0.28%	2.27%
Chinese Renminbi Debt [Member]
Debt Instrument [Line Items]
Long-term debt									$ 4,000,000	$ 4,000,000	$ 4,000,000
3.7% Notes due fiscal 2022 [Member]
Debt Instrument [Line Items]
Debt maturity date										Jul. 15, 2022
Debt instrument, interest rate									3.70%	3.70%	3.70%
Registered unsecured notes issued					$ 350,000,000
Debt instrument, discount					$ 1,000,000
Proceeds from issuance of unsecured notes										$ 347,000,000
Debt instrument due, year										2022	2022
3.7% Notes due fiscal 2022 [Member] | Fixed Rate Debt [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate					3.70%
Debt instrument due, year										2022
3.4% Notes due fiscal 2026 [Member]
Debt Instrument [Line Items]
Debt maturity date										Sep. 15, 2026
Debt instrument, interest rate									3.40%	3.40%	3.40%
Registered unsecured notes issued			$ 250,000,000
Debt instrument, discount			$ 1,000,000
Proceeds from issuance of unsecured notes										$ 248,000,000
Debt instrument due, year										2026	2026
3.4% Notes due fiscal 2026 [Member] | Fixed Rate Debt [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate			3.40%
Debt instrument due, year										2026
4.0% Notes due 2029 [Member]
Debt Instrument [Line Items]
Debt issuance cost	$ 3,000,000
Debt maturity date	Jul. 1, 2029
Debt instrument, interest rate	4.00%								4.00%	4.00%	4.00%
Registered unsecured notes issued	$ 300,000,000
Debt instrument, discount	1,000,000
Proceeds from issuance of unsecured notes	$ 296,000,000
Debt instrument due, year	2029									2029	2029
Scenario, Forecast [Member]
Debt Instrument [Line Items]
Debt instrument, covenant, ratio of consolidated total debt to consolidated EBITDA						4.50	4.50	4.50
Debt instrument, covenant, sum of subsidiary indebtedness and priority indebtedness as percentage of net worth, maximum						10.00%	10.00%	10.00%
Debt instrument, covenant, sum of subsidiary indebtedness and priority indebtedness as percentage of net worth, minimum						5.00%	5.00%	5.00%
Maximum [Member]
Debt Instrument [Line Items]
Debt instrument, covenant, ratio of consolidated total debt to consolidated EBITDA													3.50
Revolving Credit Facility, expires fiscal 2023 [Member]
Debt Instrument [Line Items]
Amount available under credit facility									$ 986,000,000	$ 986,000,000
Revolving credit facility, weighted average interest rate									1.24%	1.24%
Revolving credit facility, committed amount																$ 1,000,000,000
Debt instrument, maturity date										Oct. 23, 2022
Debt instrument due, year										2023	2023
Revolving Credit Facility - Canada, expires fiscal 2021 [Member]
Debt Instrument [Line Items]
Revolving credit facility, weighted average interest rate									0.68%	0.68%
Revolving credit facility, committed amount															$ 100,000,000
Debt instrument, maturity date										Sep. 24, 2021
Credit agreement, available borrowing									$ 100,000,000	$ 100,000,000
Debt instrument due, year										2021	2021
Revolving Credit Facility - Euro, expires fiscal 2024 [Member]
Debt Instrument [Line Items]
Revolving credit facility, weighted average interest rate									1.90%	1.90%
Revolving credit facility, committed amount | €														€ 300,000,000
Debt instrument, maturity date										May 22, 2024
Credit agreement, available borrowing									$ 204,000,000	$ 204,000,000
Debt issuance cost										$ 1,000,000
Debt instrument due, year										2024	2024
Standby Letters of Credit [Member]
Debt Instrument [Line Items]
Debt instrument due, year										2022
Standby letters of credit, outstanding amount									$ 6,000,000	$ 6,000,000

Debt and Other Obligations - _3

Debt and Other Obligations - Schedule of Future Years Payment (Detail) $ in Millions	Sep. 30, 2020USD ($)
Debt Disclosure [Abstract]
2021	$ 4
2022	365
2024	148
Thereafter	558
Total	$ 1,075

Financial Instruments and Fai_2

Financial Instruments and Fair Value Measurements - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
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	1,180,000,000	1,100,000,000
Fixed Rate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of long-term debt	1,080,000,000	1,030,000,000
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	11,000,000	10,000,000
Significant Observable Inputs (Level 2) [Member] | Foreign Currency Risks [Member] | Prepaid Expenses and Other Current Assets and Other Liabilities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivative assets (liabilities), at fair Value, net	$ (1,000,000)	$ 1,000,000

Derivatives - Additional Inform

Derivatives - Additional Information (Detail)	12 Months Ended
	Sep. 30, 2020USD ($)Derivative	Sep. 30, 2019USD ($)Derivative
Derivative [Line Items]
Significant concentration of credit risk associated with our derivative instruments	$ 0	$ 0
Cross Currency Swaps [Member]
Derivative [Line Items]
Fair value of swaps, net asset		$ 1,000,000
Fair value of swaps, net liability	$ 1,000,000
Fair Value Hedging [Member] | Interest Rate Swap-Fixed to Variable [Member] | Interest Rate Risk [Member]
Derivative [Line Items]
Derivatives held to manage interest rate risk | Derivative	0	0
Net Investment Hedge [Member] | Cross Currency Swaps [Member]
Derivative [Line Items]
Notional Amount	$ 250,000,000
Net cash interest received	4,000,000	$ 4,000,000
Cumulative gain (loss) related to swaps	$ 2,000,000	$ 5,000,000
Net Investment Hedge [Member] | Cross Currency Swaps [Member] | Fixed Rate Debt [Member]
Derivative [Line Items]
Derivative Instruments Frequency of Cash Settlements	semi-annually

Derivatives - Details of Deriva

Derivatives - Details of Derivatives Held to Manage Foreign Currency Risk (Detail)		Sep. 30, 2020USD ($)	Sep. 30, 2020EUR (€)	Sep. 30, 2019USD ($)	Sep. 30, 2019EUR (€)	Sep. 30, 2016
3.4% Notes [Member]
Derivative [Line Items]
Interest rate on borrowing		3.40%	3.40%	3.40%	3.40%
3.4% Notes [Member] | Fixed Rate Debt [Member]
Derivative [Line Items]
Interest rate on borrowing						3.40%
Net Investment Hedge [Member] | Cross Currency Swaps [Member]
Derivative [Line Items]
Notional Amount		$ 250,000,000
Net Investment Hedge [Member] | 3.4% Notes [Member] | Cross Currency Swaps [Member]
Derivative [Line Items]
Notional Amount		$ 250,000,000	€ 233,000,000	$ 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]	$ 54,000,000		$ 54,000,000
[1]	As of September 30, 2020, Cabot’s forward foreign exchange contracts were denominated in Canadian dollar, Indonesian rupiah and Czech koruna. As of September 30, 2019, Cabot’s forward foreign exchange contracts were denominated in British pound, Canadian dollar, Indonesian rupiah and Czech koruna.

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	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments Gain Loss [Line Items]
Gain/(Loss) Recognized in AOCI	$ 1	$ 23	$ (2)
(Gain)/Loss Reclassified from AOCI into Interest Expense in the Consolidated Statements of Operations	(5)	(5)	(5)
(Gain)/Loss Recognized in Interest Expense in the Consolidated Statements of Operations (Amount Excluded from Effectiveness Testing)	$ 2	$ 1	$ 2

Hyperinflationary Economies - A

Hyperinflationary Economies - Additional Information (Detail) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019USD ($)	Sep. 30, 2020USD ($)$ / $	Sep. 30, 2019USD ($)$ / $	Sep. 30, 2018USD ($)$ / $
Other Nonoperating Income (Expense) [Member]
Schedule Of Equity Method Investments [Line Items]
Foreign currency transaction gain (loss)		$ (6)		$ (4)
Maximum [Member] | Other Nonoperating Income (Expense) [Member]
Schedule Of Equity Method Investments [Line Items]
Foreign currency transaction gain (loss)			$ 1
Argentina [Member]
Schedule Of Equity Method Investments [Line Items]
Percentage of net revenue		2.00%	3.00%	2.00%
Foreign currency exchange rate, translation | $ / $		76.12	57.32	39.70
Argentina [Member] | Other Nonoperating Income (Expense) [Member]
Schedule Of Equity Method Investments [Line Items]
Foreign currency transaction gain (loss)		$ (2)	$ 2	$ 3
Argentina [Member] | Maximum [Member]
Schedule Of Equity Method Investments [Line Items]
Percentage of assets and liabilities current		2.00%	2.00%
Venezuela [Member] | Carbon Black Affiliate [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment, ownership percentage	49.00%
Venezuela [Member] | Other Nonoperating Income (Expense) [Member] | Carbon Black Affiliate [Member]
Schedule Of Equity Method Investments [Line Items]
Impairment charge	$ 11
Carbon Black Operating Entity [Member] | Argentina [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method investment, ownership percentage		100.00%

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2020USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)Plan	Sep. 30, 2018USD ($)
Defined Benefit Plan Disclosure [Line Items]
Number of foreign defined benefit plans | Plan					1
Pre-tax gain from net pension obligations					$ 7
Additional charge on defined benefit plan actuarial gain (loss)					3
Defined contribution plans expenses				$ 19	20	$ 19
Pension Benefits [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected contribution			$ 5
Postretirement Benefits [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Postretirement medical benefits			$ 4
U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		$ 99		99	157
Settlement loss		$ 3
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Settlement Gain (Loss), Statement of Income or Comprehensive Income [Extensible List]		us-gaap:OtherNonoperatingIncomeExpenseMember
Pension benefit obligation decreased				47
U.S. Defined Benefit Plans [Member] | Scenario, Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement loss	$ 6
Defined Benefit Plan, Net Periodic Benefit (Cost) Credit, Settlement Gain (Loss), Statement of Income or Comprehensive Income [Extensible List]	us-gaap:OtherNonoperatingIncomeExpenseMember
U.S. Defined Benefit Plans [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement loss				3
Pre-tax gain from net pension obligations		$ (6)		(6)	(13)
U.S. Defined Benefit Plans [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax gain from net pension obligations		4		4	6
Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation		215		$ 215	205
Pension benefit obligation decreased					139
Foreign Plans [Member] | Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				41.00%
Foreign Plans [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				49.00%
Foreign Plans [Member] | Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				6.00%
Foreign Plans [Member] | Cash and Other Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of weighted-average target asset allocation				4.00%
Foreign Plans [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement loss				$ 1	(7)
Pre-tax gain from net pension obligations		(40)		(40)	(36)
Foreign Plans [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pre-tax gain from net pension obligations		$ (4)		$ (4)	(6)
U.K. Plan [Member] | Other Nonoperating Income (Expense) [Member]
Defined Benefit Plan Disclosure [Line Items]
Charge on effect of accrued benefit					$ 2

Employee Benefit Plans - Change

Employee Benefit Plans - Change in Projected Benefit Obligations and Change in Plan Assets (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Change in Plan Assets:
Fair value of plan assets at beginning of year	$ 346
Fair value of plan assets at end of year	300	$ 346
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Change in Benefit Obligations:
Benefit obligation at beginning of year	157	143
Service cost	1	1	$ 1
Interest cost	4	5	5
Loss from changes in actuarial assumptions and plan experience	2	21
Benefits paid	(7)	(11)
Settlements or curtailments	(57)	(1)
Other	(1)	(1)
Benefit obligation at end of year	99	157	143
Change in Plan Assets:
Fair value of plan assets at beginning of year	151	149
Actual return on plan assets	9	14
Employer contribution	1	1
Benefits paid	(7)	(11)
Settlements	(57)	(1)
Expenses paid from assets	(1)	(1)
Fair value of plan assets at end of year	96	151	149
Funded status	(3)	(6)
Recognized asset (liability)	(3)	(6)
Pension Benefits [Member] | Foreign Plans [Member]
Change in Benefit Obligations:
Benefit obligation at beginning of year	220	373
Service cost	5	7	9
Interest cost	3	5	7
Plan participants’ contribution	1	1
Foreign currency exchange rate changes	7	(13)
Loss from changes in actuarial assumptions and plan experience	5
Benefits paid	(8)	(7)
Settlements or curtailments	(2)	(134)
Divestiture of Specialty Fluids		(13)
Other		1
Benefit obligation at end of year	231	220	373
Change in Plan Assets:
Fair value of plan assets at beginning of year	195	323
Actual return on plan assets	7	17
Employer contribution	6	7
Plan participants’ contribution	1	1
Foreign currency exchange rate changes	5	(11)
Benefits paid	(8)	(7)
Settlements	(2)	(124)
Divestiture		(10)
Expenses paid from assets		(1)
Fair value of plan assets at end of year	204	195	323
Funded status	(27)	(25)
Recognized asset (liability)	(27)	(25)
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Change in Benefit Obligations:
Benefit obligation at beginning of year	28	29
Interest cost	1	1	1
Loss from changes in actuarial assumptions and plan experience	1	1
Benefits paid	(3)	(3)
Benefit obligation at end of year	27	28	29
Change in Plan Assets:
Employer contribution	3	3
Benefits paid	(3)	(3)
Funded status	(27)	(28)
Recognized asset (liability)	(27)	(28)
Postretirement Benefits [Member] | Foreign Plans [Member]
Change in Benefit Obligations:
Benefit obligation at beginning of year	20	19
Interest cost		1	1
Foreign currency exchange rate changes		(1)
Loss from changes in actuarial assumptions and plan experience		2
Benefits paid		(1)
Benefit obligation at end of year	20	20	$ 19
Change in Plan Assets:
Employer contribution		1
Benefits paid		(1)
Funded status	(20)	(20)
Recognized asset (liability)	$ (20)	$ (20)

Employee Benefit Plans - Assump

Employee Benefit Plans - Assumptions Used to Determine Pension Benefit Obligations and Periodic Benefit Costs, Postretirement Benefit Obligations and Net Costs (Detail)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.10%	2.60%	4.20%
Cash balance interest credit rate	0.90%	0.90%	3.30%
Discount rate - benefit obligation	2.60%	4.20%	3.60%
Discount rate - interest cost	2.60%	3.90%	3.00%
Expected long-term rate of return on plan assets	2.50%	6.30%	6.80%
Cash balance interest credit rate	0.90%	3.30%	3.30%
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	1.70%	1.80%	2.40%
Initial health care cost trend rate	3.00%	3.00%	2.70%
Cash balance interest credit rate	1.70%	1.90%	2.00%
Discount rate - benefit obligation	1.80%	2.40%	2.40%
Discount rate - service cost	1.80%	2.50%	2.40%
Discount rate - interest cost	1.60%	2.10%	2.00%
Expected long-term rate of return on plan assets	5.20%	4.90%	4.90%
Initial health care cost trend rate	3.00%	2.70%	2.70%
Cash balance interest credit rate	1.90%	2.00%	2.00%
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.10%	2.90%	4.10%
Initial health care cost trend rate	6.00%	6.50%	7.00%
Discount rate - benefit obligation	2.90%	4.10%	3.40%
Discount rate - service cost	2.60%	4.00%	3.10%
Discount rate - interest cost	2.50%	3.70%	2.80%
Initial health care cost trend rate	6.50%	7.00%	7.00%
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	2.40%	2.40%	3.20%
Initial health care cost trend rate	6.90%	6.90%	7.00%
Discount rate - benefit obligation	2.40%	3.20%	3.10%
Discount rate - service cost	2.90%	3.50%	3.60%
Discount rate - interest cost	2.30%	3.10%	3.00%
Initial health care cost trend rate	6.90%	7.00%	7.10%

Employee Benefit Plans - Amount

Employee Benefit Plans - Amounts Recognized in Consolidated Balance Sheets (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accounts payable and accrued liabilities		$ (3)
Other liabilities	$ (3)	(3)
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Other assets	21	19
Accounts payable and accrued liabilities	(2)	(1)
Other liabilities	(46)	(43)
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accounts payable and accrued liabilities	(3)	(3)
Other liabilities	(24)	(25)
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accounts payable and accrued liabilities	(1)
Other liabilities	$ (19)	$ (20)

Employee Benefit Plans - Amou_2

Employee Benefit Plans - Amounts Recognized in Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss		$ (7)
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	$ 6	13
Balance in accumulated other comprehensive income (loss), pretax	6	13
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	40	36
Balance in accumulated other comprehensive income (loss), pretax	40	36
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	(4)	(6)
Balance in accumulated other comprehensive income (loss), pretax	(4)	(6)
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net actuarial (gain) loss	4	6
Balance in accumulated other comprehensive income (loss), pretax	$ 4	$ 6

Employee Benefit Plans - Estima

Employee Benefit Plans - Estimated Future Benefit Payments (Detail) $ in Millions	Sep. 30, 2020USD ($)
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
2021	$ 96
2026 - 2030	1
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
2021	12
2022	10
2023	10
2024	12
2025	11
2026 - 2030	57
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
2021	3
2022	3
2023	3
2024	2
2025	2
2026 - 2030	9
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
2021	1
2022	1
2023	1
2024	1
2025	1
2026 - 2030	$ 4

Employee Benefit Plans - Esti_2

Employee Benefit Plans - Estimated Future Benefit Payments (Parenthetical) (Detail) $ in Millions	Sep. 30, 2020USD ($)
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan payment	$ 96

Employee Benefit Plans - Net Pe

Employee Benefit Plans - Net Periodic Defined Benefit Pension and Other Postretirement Benefit Costs (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 1	$ 1
Interest cost	4	5	5
Expected return on plan assets	(3)	(9)	(10)
Settlements or Curtailments cost	3
Net periodic (benefit) cost	5	(3)	(4)
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	7	9
Interest cost	3	5	7
Expected return on plan assets	(9)	(10)	(15)
Amortization of prior service cost		2
Net losses	3	2	3
Settlements or Curtailments cost	1	(7)
Net periodic (benefit) cost	3	(1)	4
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	1	1
Amortization of prior service cost		(2)	(3)
Net losses	(1)	(1)	(1)
Net periodic (benefit) cost		(2)	(3)
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Interest cost		1	1
Net losses	1
Net periodic (benefit) cost	$ 1	$ 1	$ 1

Employee Benefit Plans - Other

Employee Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss), Pre-Tax (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
(Loss) gain on settlements	$ (3)
Pension Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		$ (4)	$ 14	$ (4)
(Loss) gain on settlements		(3)
Net changes recognized in Total other comprehensive (income) loss		(7)	14	(4)
Pension Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		8	(16)
Prior service (credit) cost			3
Amortization of prior service credit			(2)
Amortization of prior unrecognized loss		(3)	(2)	(3)
Loss on divestiture			(2)
(Loss) gain on settlements		(1)	7
Net changes recognized in Total other comprehensive (income) loss		4	(12)	(3)
Postretirement Benefits [Member] | U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		1		(2)
Amortization of prior service credit			2	3
Amortization of prior unrecognized loss		1	1	1
Net changes recognized in Total other comprehensive (income) loss		2	3	2
Postretirement Benefits [Member] | Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net (gains) losses		(1)	2	(1)
Amortization of prior unrecognized loss		(1)
Net changes recognized in Total other comprehensive (income) loss		$ (2)	$ 2	$ (1)

Employee Benefit Plans - Othe_2

Employee Benefit Plans - Other Changes in Plan Assets and Benefit Obligations Recognized in Other Comprehensive Income (Loss), Pre-Tax (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Other Comprehensive (Income) Loss, pension and other postretirement tax benefit (provision)		$ 5	$ (1)
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Other Comprehensive (Income) Loss, pension and other postretirement tax benefit (provision)	$ (1)

Employee Benefit Plans - Define

Employee Benefit Plans - Defined Benefit Pension Plans Weighted-Average Asset Allocations (Detail)	Sep. 30, 2020	Sep. 30, 2019
U.S. Defined Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Debt securities	95.00%	68.00%
Cash and other securities	5.00%	32.00%
Total	100.00%	100.00%
Foreign Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity securities	39.00%	39.00%
Debt securities	50.00%	50.00%
Real estate	6.00%	6.00%
Cash and other securities	5.00%	5.00%
Total	100.00%	100.00%

Employee Benefit Plans - Fair V

Employee Benefit Plans - Fair Value of Pension Plan Assets by Asset Category (Detail) - USD ($) $ in Millions		Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		$ 300	$ 346
Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		107	10
Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		184	328
Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		5	6
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		111	164
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		106	9
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	152
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets			1
Significant Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		189	182
Significant Observable Inputs (Level 2) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	1
Significant Observable Inputs (Level 2) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		183	176
Significant Observable Inputs (Level 2) [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		5	5
Cash and Cash Equivalent Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		4	2
Cash and Cash Equivalent Funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		4	2
U.S. Government Bonds [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		12
U.S. Government Bonds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		12
U.S. Corporate Bonds [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		84
U.S. Corporate Bonds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		84
Non-U.S. Equities [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		4	3
Non-U.S. Equities [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		4	3
Equity Funds [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	76	74
Equity Funds [Member] | Significant Observable Inputs (Level 2) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[1]	76	74
Non-U.S. Government Bonds [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		2	2
Non-U.S. Government Bonds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		2	2
Fixed Income Funds [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[2]	95	194
Fixed Income Funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[2]		104
Fixed Income Funds [Member] | Significant Observable Inputs (Level 2) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[2]	95	90
Non-U.S. Corporate Bonds [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		3	3
Non-U.S. Corporate Bonds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		3	3
Real Estate [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[3]	12	12
Real Estate [Member] | Significant Observable Inputs (Level 2) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[3]	12	12
Mortgage Backed Securities [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	1
Mortgage Backed Securities [Member] | Significant Observable Inputs (Level 2) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	1
Other Fixed Income [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	1
Other Fixed Income [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Direct Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	1
Cash Equivalent Funds [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	48
Cash Equivalent Funds [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Total Investment Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets		1	48
Insurance Contracts [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[4]	5	5
Insurance Contracts [Member] | Significant Observable Inputs (Level 2) [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets	[4]	$ 5	5
Other Alternative Investments [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets			1
Other Alternative Investments [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension plan assets			$ 1
[1]	The equity funds asset class includes funds that invest in U.S. equities as well as equity securities issued by companies incorporated, listed or domiciled in countries in developed and/or emerging markets. These companies may be in the small-, mid- or large-cap categories.
[2]	The fixed income funds asset class includes investments in high quality funds. High quality fixed income funds primarily invest in low risk U.S. and non-U.S. government securities, investment-grade corporate bonds, mortgages and asset-backed securities. A significant portion of the fixed income funds include investment in long-term bond funds.
[3]	The real estate funds asset class includes funds that primarily invest in entities which are principally engaged in the ownership, acquisition, development, financing, sale and/or management of income-producing real estate properties, both commercial and residential. These funds typically seek long-term growth of capital and current income that is above average relative to public equity funds.
[4]	Insurance contracts held by the Company’s non-U.S. plans are issued by well-known, highly rated insurance companies.

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2020		Sep. 30, 2019	Sep. 30, 2018	Mar. 09, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of vesting in first anniversary	30.00%
Percentage of vesting in second anniversary	30.00%
Percentage of vesting in third anniversary	40.00%
Net stock-based compensation expense	$ 9,000,000		$ 8,000,000	$ 16,000,000
(Provision) benefit for income taxes	$ 191,000,000		70,000,000	193,000,000
Stock Options, Weighted Average Grant Date Fair Value, Granted	$ 10.68
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of exercise price equal to market price on the date of grant	100.00%
Vesting period (in years)	3 years
Expiration period, years	10 years
Unrecognized compensation cost	$ 2,000,000
Weighted-average period, years	1 year
Options outstanding, aggregate intrinsic value	$ 0
Options exercisable, aggregate intrinsic value	$ 0
Closing stock price	$ 36.03
Intrinsic value of options exercised			1,000,000	11,000,000
Cash received from exercises	$ 1,000,000		$ 2,000,000	22,000,000
(Provision) benefit for income taxes				$ 1,000,000
Stock Options, Weighted Average Grant Date Fair Value, Granted	$ 10.68		$ 10.85	$ 15.21
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period (in years)	3 years
Unrecognized compensation cost	$ 10,000,000
Weighted-average period, years	1 year
Estimated weighted average grant date fair value	$ 49.36	[1]	$ 49.44	$ 62.18
Intrinsic value of restricted stock units vested	$ 13,000,000		$ 18,000,000	$ 12,000,000
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period (in years)	3 years
2017 Long-Term Incentive Plan [Member] | Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, authorized shares					5,375,000
Supplemental 401(k) Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Supplemental retirement savings plan, aggregate value of the accounts, shares	76,000		93,000
Supplemental retirement savings plan aggregate value of the accounts paid in cash			$ 1,000,000
[1]	The number granted represents the number of shares issuable upon vesting of time-based restricted stock units and performance-based restricted stock units, assuming the Company performs at the target performance level in each year of the three-year performance period.

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expenses (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense before tax	$ 9	$ 11	$ 22
Income tax benefit		(3)	(6)
Net stock-based compensation expense	9	8	16
Cost of Sales [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense before tax	1	1	2
Selling and Administrative Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense before tax	7	9	19
Research and Technical Expenses [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation expense before tax	$ 1	$ 1	$ 1

Stock-Based Compensation - Equi

Stock-Based Compensation - Equity Incentive Plan Activity (Detail) - $ / shares shares in Thousands		12 Months Ended
		Sep. 30, 2020		Sep. 30, 2019	Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Options, Total Options, Outstanding at September 30, 2018	[1]	1,022
Stock Options, Total Options, Granted	[1]	333
Stock Options, Total Options, Exercised / Vested	[1]	(29)
Stock Options, Total Options, Cancelled / Forfeited	[1]	(53)
Stock Options, Total Options, Outstanding at September 30, 2019	[1]	1,273	[2]	1,022
Stock Options, Total Options, Exercisable at September 30, 2019	[1]	664
Stock Options, Weighted Average Exercise Price, Outstanding at September 30, 2018		$ 50.57
Stock Options, Weighted Average Exercise Price, Granted		50.23
Stock Options, Weighted Average Exercise Price, Exercised / Vested		46.76
Stock Options, Weighted Average Exercise Price, Cancelled / Forfeited		53.60
Stock Options, Weighted Average Exercise Price, Outstanding at September 30, 2019		50.45	[2]	$ 50.57
Stock Options, Weighted Average Exercise Price, Exercisable at September 30, 2019		49.59
Stock Options, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2018		12.13
Stock Options, Weighted Average Grant Date Fair Value, Granted		10.68
Stock Options, Weighted Average Grant Date Fair Value, Exercised / Vested		6.07
Stock Options, Weighted Average Grant Date Fair Value, Cancelled / Forfeited		7.07
Stock Options, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2019		$ 11.74	[2]	$ 12.13
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted Stock / Units, Outstanding at September 30, 2018	[3]	765
Restricted Stock / Units, Granted	[3]	276
Restricted Stock / Units, Performance-based adjustment	[3],[4]	(102)
Restricted Stock / Units, Exercised / Vested	[3]	(261)
Restricted Stock / Units, Cancelled / Forfeited	[3]	(74)
Restricted Stock / Units, Outstanding at September 30, 2019	[3]	604	[2]	765
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2018	[3]	$ 53.71
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Granted		49.36	[3]	$ 49.44	$ 62.18
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Performance-based adjustment	[3],[4]	53.02
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Exercised / Vested	[3]	50.67
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Cancelled / Forfeited	[3]	55.74
Restricted Stock / Units, Weighted Average Grant Date Fair Value, Outstanding at September 30, 2019	[3]	$ 52.87	[2]	$ 53.71
[1]	Unvested stock options were approximately 609,000 51.38
[2]	Stock options outstanding include options vested and expected to vest in the future and have a weighted average remaining contractual life of 6.66
[3]	The number granted represents the number of shares issuable upon vesting of time-based restricted stock units and performance-based restricted stock units, assuming the Company performs at the target performance level in each year of the three-year performance period.
[4]	Represents the net incremental number of shares cancelled based on the Company’s actual financial performance metrics for fiscal 20 20 .

Stock-Based Compensation - Eq_2

Stock-Based Compensation - Equity Incentive Plan Activity (Parenthetical) (Detail) - $ / shares shares in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock options outstanding include options vested and expected to vest in the future, weighted average remaining contractual life, in years	6 years 7 months 28 days
Unvested stock options	609,000	523,000
Unvested stock options, weighted average grant date fair value	$ 51.38	$ 52.95

Stock-Based Compensation - Weig

Stock-Based Compensation - Weighted-Average Assumptions (Detail) - $ / shares	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected stock price volatility	28.00%	27.00%	28.00%
Risk free interest rate	1.90%	3.10%	2.20%
Expected life of options (years)		6 years	6 years
Expected annual dividends per year	$ 1.40	$ 1.32	$ 1.26

Restructuring - Recorded Restru

Restructuring - Recorded Restructuring Activities (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Restructuring Cost And Reserve [Line Items]
Restructuring reserve, period expense	$ 19	$ 16	$ (30)
Cost of Sales [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring reserve, period expense	6	9	(31)
Selling and Administrative Expenses [Member]
Restructuring Cost And Reserve [Line Items]
Restructuring reserve, period expense	$ 13	$ 7	$ 1

Restructuring - Restructuring A

Restructuring - Restructuring Activities and Related Reserves (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Restructuring Cost And Reserve [Line Items]
Reserve balance	$ 7	$ 5	$ 3
Charges (gain)	19	16	(30)
Costs charged against assets (liabilities)	(1)	(2)	(2)
Cash (paid) received	(16)	(12)	34
Reserve balance	9	7	5
Severance and Employee Benefits [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	3	1	1
Charges (gain)	14	11	2
Cash (paid) received	(12)	(9)	(2)
Reserve balance	5	3	1
Environmental Remediation and Decommissioning Activities [Member]
Restructuring Cost And Reserve [Line Items]
Reserve balance	4	4	2
Charges (gain)			3
Cash (paid) received			(1)
Reserve balance	4	4	4
Non-Cash Asset Impairment and Accelerated Depreciation [Member]
Restructuring Cost And Reserve [Line Items]
Charges (gain)	1	2	1
Costs charged against assets (liabilities)	(1)	(2)	(1)
Asset Sales [Member]
Restructuring Cost And Reserve [Line Items]
Charges (gain)			(38)
Costs charged against assets (liabilities)			(1)
Cash (paid) received			39
Other [Member]
Restructuring Cost And Reserve [Line Items]
Charges (gain)	4	3	2
Cash (paid) received	$ (4)	$ (3)	$ (2)

Restructuring - Additional Info

Restructuring - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Restructuring Cost And Reserve [Line Items]
Restructuring Charges	$ 19	$ 16	$ (30)
Proceeds from the sale of land			39
2020 Reorganization [Member]
Restructuring Cost And Reserve [Line Items]
Severance costs	17
Restructuring charges expected in fiscal 2021 related to site demolition and clearing costs	1
Restructuring charges expected thereafter fiscal year related to site demolition and clearing costs	3
Restructuring cash payments of fiscal year	13
Restructuring cash payments in fiscal 2021	4
Restructuring future cash payments thereafter fiscal year	4
Accrued severance charges	4
Purification Solutions Transformation Plan [Member]
Restructuring Cost And Reserve [Line Items]
Severance costs	2	8
Restructuring charges expected in fiscal 2021 related to site demolition and clearing costs	1
Restructuring cash payments of fiscal year	2	8
Restructuring cash payments in fiscal 2021	2
Restructuring future cash payments thereafter fiscal year	2
Accrued severance charges	1
Restructuring Charges		9
Professional fees and other charges		$ 1
Restructuring charges expected thereafter fiscal 2021 related to site demolition and clearing costs	$ 1
Operational Restructuring [Member] | Thane, India [Member]
Restructuring Cost And Reserve [Line Items]
Proceeds from the sale of land			28
Net benefit to earnings			28
Operational Restructuring [Member] | Merak, Indonesia [Member] | Cost of Sales [Member]
Restructuring Cost And Reserve [Line Items]
Proceeds from the sale of land			13
Net benefit to earnings			$ 11

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) - Changes in Each Component of AOCI, Net of Tax (Detail) - USD ($) $ in Millions	Oct. 01, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 1,134	$ 1,134	$ 1,279	$ 1,625
Adoption of accounting standards	2
Ending Balance		814	1,134	1,279
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(338)	(338)	(266)
Other comprehensive income (loss) before reclassifications		42	(69)
Amounts reclassified from AOCI		(3)	(9)
Adoption of accounting standards		(3)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		5	(6)
Ending Balance		(307)	(338)	(266)
Unrealized Gains on Investment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	1	1	1
Adoption of accounting standards		(1)
Ending Balance			1	1
Pension and Other Postretirement Benefit Liability Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(54)	(54)	(52)
Other comprehensive income (loss) before reclassifications		3	4
Amounts reclassified from AOCI		6	(6)
Adoption of accounting standards		1
Ending Balance		(44)	(54)	(52)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ (391)	(391)	(317)	(259)
Other comprehensive income (loss) before reclassifications		45	(65)
Amounts reclassified from AOCI		3	(15)	(3)
Adoption of accounting standards		(3)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		5	(6)
Ending Balance		$ (351)	$ (391)	$ (317)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified Out of AOCI (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
(Gains) Losses Reclassified to Interest Expense [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (5)	$ (5)	$ (5)
(Gains) Losses Excluded from Effectiveness Testing and Amortized to Interest Expense [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	2	1	2
Amortization of Actuarial Losses and Prior Service Cost (Credit) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	3	1	(1)
Settlement and Curtailment Loss (Gain)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	4	(7)
Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	4	(13)	(4)
Tax impact	(1)	(2)	1
Total after tax	$ 3	(15)	$ (3)
Specialty Fluids Divestiture [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		$ (3)

Earnings Per Share - Components

Earnings Per Share - Components of Basic and Diluted Earnings Per Common Share (EPS) (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Basic EPS:
Net income (loss) attributable to Cabot Corporation	$ (272)	$ (6)	$ (1)	$ 41	$ 33	$ 32	$ 23	$ 69	$ (238)	$ 157	$ (113)
Less: Dividends and dividend equivalents to participating securities										1	1
Less: Undistributed earnings allocated to participating securities										1
Earnings (loss) allocated to common shareholders (numerator)									$ (238)	$ 155	$ (114)
Weighted average common shares and participating securities outstanding									57.3	59.5	62.4
Less: Participating securities									0.7	0.8	0.7
Adjusted weighted average common shares (denominator)									56.6	58.7	61.7
Basic	$ (4.81)	$ (0.12)	$ (0.01)	$ 0.71	$ 0.56	$ 0.55	$ 0.39	$ 1.14	$ (4.21)	$ 2.64	$ (1.85)
Diluted EPS:
Earnings (loss) allocated to common shareholders									$ (238)	$ 155	$ (114)
Plus: Earnings allocated to participating securities										2
Less: Adjusted earnings allocated to participating securities										2
Earnings (loss) available to common shares (numerator)									$ (238)	$ 155	$ (114)
Adjusted weighted average common shares outstanding									56.6	58.7	61.7
Common shares issuable										0.1
Adjusted weighted average common shares (denominator)									56.6	58.8	61.7
Diluted	$ (4.81)	$ (0.12)	$ (0.01)	$ 0.70	$ 0.55	$ 0.55	$ 0.39	$ 1.14	$ (4.21)	$ 2.63	$ (1.85)

Earnings Per Share - Calculatio

Earnings Per Share - Calculation of Undistributed Earnings (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income (loss) attributable to Cabot Corporation	$ (272)	$ (6)	$ (1)	$ 41	$ 33	$ 32	$ 23	$ 69	$ (238)	$ 157	$ (113)
Less: Dividends declared on common stock									80	80	79
Less: Dividends and dividend equivalents to participating securities										1	1
Undistributed earnings (loss)									(318)	76	(193)
Undistributed earnings (loss) allocated to common shareholders									$ (318)	75	$ (193)
Undistributed earnings allocated to participating securities										$ 1

Earnings Per Share - Componen_2

Earnings Per Share - Components of Basic and Diluted Earnings Per Common Share (Parenthetical) (Detail) - shares	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share	1,821,018	942,060	229,220

Income Taxes - Income Before In

Income Taxes - Income Before Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments [Abstract]
Domestic	$ (274)	$ (66)	$ (229)
Foreign	241	321	346
Income (loss) from continuing operations before income taxes and equity in earnings of affiliated companies	$ (33)	$ 255	$ 117

Income Taxes - Provision (Benef

Income Taxes - Provision (Benefit) for Income Taxes (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
U.S. federal and state, Current	$ (1)	$ 2	$ 14
U.S. federal and state, Deferred	139	(30)	114
U.S. federal and state, Total	138	(28)	128
Foreign, Current	62	95	88
Foreign, Deferred	(9)	3	(23)
Foreign, Total	53	98	65
Provision (benefit) for income taxes	$ 191	$ 70	$ 193

Income Taxes - Reconciliation U

Income Taxes - Reconciliation Using U.S. Statutory Rate (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Computed tax expense at the federal statutory rate	$ (7)	$ 53	$ 29
Foreign impact of taxation at different rates, repatriation, valuation allowance, and other	4	17	(8)
Impact of the Tax Cuts and Jobs Act of 2017			159
Global Intangible Low Taxed Income (GILTI)	(4)	10
Impact of the Coronavirus Aid, Relief, and Economic Security ("CARES") Act of 2020	(10)
Impact of increase (decrease) in valuation allowance on U.S. deferred taxes	228
U.S. and state benefits from research and experimentation activities	(2)	(2)	(2)
Provision (settlement) of unrecognized tax benefits	(7)	(8)	1
Impact of goodwill impairment charge			18
Permanent differences, net		1	(1)
State taxes, net of federal effect	(11)	(1)	(3)
Provision (benefit) for income taxes	$ 191	$ 70	$ 193

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jul. 31, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Oct. 01, 2019	Sep. 30, 2017
Income Taxes [Line Items]
Valuation allowance		$ 317	$ 124
NOLs		653
Foreign tax credit carry forwards		58	20
R&D credit carryforwards		44	43
Other business credit carryforwards		23	29
Increased/(decreased) valuation allowance			(45)
Other tax credit carryforwards		125
Undistributed earnings		1,631
Unrecognized tax benefits		23	27	$ 37		$ 36
Unrecognized tax benefits, recorded		14
Unrecognized tax benefits, not recorded		9
Accruals for penalties		1
Accruals for interest		3
Total penalties and interest		1	$ 2	$ 2
Favorable impact on tax provision		$ 23
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
Non-U.S. Jurisdictions [Member]
Income Taxes [Line Items]
NOLs		$ 32
Increased/(decreased) valuation allowance		$ (32)
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		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
Specialty Fluids [Member]
Income Taxes [Line Items]
Operating losses subject to expiration		$ 16
U.S. Defined Benefit Plans [Member]
Income Taxes [Line Items]
Valuation allowance		253
NOLs		18
Foreign tax credit carry forwards		58
R&D credit carryforwards		44
State tax credits		19
Other business credit carryforwards		114
Increased/(decreased) valuation allowance		193
Net deferred tax assets		228
U.S. Defined Benefit Plans [Member] | Originated in Prior Year [Member]
Income Taxes [Line Items]
Net deferred tax assets					$ 132
U.S. Defined Benefit Plans [Member] | Originated in Current Year [Member]
Income Taxes [Line Items]
Net deferred tax assets		96
Minimum [Member]
Income Taxes [Line Items]
Foreign tax rate	90.00%
Maximum [Member] | Non-U.S. Jurisdictions [Member]
Income Taxes [Line Items]
Other tax credit carryforwards		$ 1

Income Taxes - Components of De

Income Taxes - Components of Deferred Income Taxes (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Components Of Deferred Tax Assets [Abstract]
Deferred expenses	$ 19	$ 15
Intangible assets	37	28
Inventory	13	9
Operating lease liability	20
Other	32	3
Pension and other benefits	35	41
Net operating loss carryforwards	109	124
Foreign tax credit carryforwards	58	20
R&D credit carryforwards	44	43
Other business credit carryforwards	23	29
Subtotal	390	312
Valuation allowance	(317)	(124)
Total deferred tax assets	73	188
Property, plant and equipment	(40)	(61)
Right of use asset	(20)
Unremitted earnings of non-U.S. subsidiaries	(18)	(5)
Total deferred tax liabilities	$ (78)	$ (66)

Income Taxes - Expiration Dates

Income Taxes - Expiration Dates of NOLs and Other Tax Credit Carryforwards Before Valuation Allowances (Detail) $ in Millions	Sep. 30, 2020USD ($)
Significant Tax Attributes And Dates Of Expiration [Line Items]
NOLs	$ 653
Credits	125
2021 - 2027 [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
NOLs	168
Credits	50
2028 and thereafter [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
NOLs	198
Credits	73
Indefinite Carryforwards [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
NOLs	287
Credits	$ 2

Income Taxes - Expiration Dat_2

Income Taxes - Expiration Dates of NOLs and Other Tax Credit Carryforwards Before Valuation Allowances (Parenthetical) (Detail)	12 Months Ended
	Sep. 30, 2020
Significant Tax Attributes And Dates Of Expiration [Line Items]
Expiration periods	2028
Minimum [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
Expiration periods	2021
Maximum [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
Expiration periods	2027

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Balance at beginning of the year	$ 27	$ 37	$ 36
Additions based on tax provisions related to the current year	2		2
Additions for tax positions of prior years	2		1
Reductions of tax provisions of prior years	(1)	(1)
Reductions related to settlements	(5)	(5)
Reductions from lapse of statute of limitations	(2)	(4)	(2)
Balance at end of the year	$ 23	$ 27	$ 37

Leases - Additional Information

Leases - Additional Information (Detail) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)
Lessee Lease Description [Line Items]
Short term lease costs	$ 6
Variable lease cost	$ 1
Minimum [Member]
Lessee Lease Description [Line Items]
Lease term	1 year
Maximum [Member]
Lessee Lease Description [Line Items]
Lease term	19 years
Lease extension period	15 years
Maximum [Member] | Land [Member]
Lessee Lease Description [Line Items]
Lease term	70 years

Leases - Components of Company'

Leases - Components of Company's Lease Costs (Detail) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)
Leases [Abstract]
Operating lease cost	$ 32
Finance lease cost	6
Total lease cost	$ 38

Leases - Supplemental Cash Flow

Leases - Supplemental Cash Flow Information Related to Company's Leases (Detail) $ in Millions	12 Months Ended
	Sep. 30, 2020USD ($)
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 25
Operating cash flows from finance leases	2
Financing cash flows from finance leases	3
Right-of-use assets obtained in exchange for new operating lease liabilities	14
Right-of-use assets obtained in exchange for new finance lease liabilities	$ 24

Leases - Supplemental Balance S

Leases - Supplemental Balance Sheet Information Related to Company's Leases (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Oct. 01, 2019
Lease ROU assets:
Operating	$ 98	$ 106
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsNoncurrent
Finance	$ 44
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:PropertyPlantAndEquipmentNet
Total lease ROU assets	$ 142
Lease liabilities:
Operating	$ 15
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:AccountsPayableAndAccruedLiabilitiesCurrent
Finance	$ 3
Finance Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtCurrent
Operating	$ 89
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherLiabilitiesNoncurrent
Finance	$ 28
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:LongTermDebtNoncurrent
Total lease liabilities	$ 135

Leases - Weighed Average Remain

Leases - Weighed Average Remaining Lease Term and Discount Rates (Detail)	Sep. 30, 2020
Lease Cost [Abstract]
Operating leases	17 years
Finance leases	12 years
Operating leases	2.19%
Finance leases	4.42%

Leases - Future Minimum Lease P

Leases - Future Minimum Lease Payments Under Non-cancelable Operating and Finance Leases (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Oct. 01, 2019	Sep. 30, 2019
Operating leases
2021	$ 17
2022	12
2023	11
2024	10
2025	9
2026 and thereafter	67
Total lease payments	126
Less: imputed interest	22
Operating lease liability	$ 104	$ 111
Operating Lease, Liability, Statement of Financial Position [Extensible List]	cbt:AccountsPayableAndAccruedLiabilitiesAndOtherLiabilitiesMember	cbt:AccountsPayableAndAccruedLiabilitiesAndOtherLiabilitiesMember
Finance leases
2021	$ 5
2022	4
2023	4
2024	4
2025	4
2026 and thereafter	19
Total lease payments	40
Less: imputed interest	9
Total	$ 31		$ 12

Leases - Future Minimum Lease_2

Leases - Future Minimum Lease Payments Under Non-cancelable Leases (Detail) $ in Millions	Sep. 30, 2019USD ($)
Operating leases
2020	$ 23
2021	14
2022	9
2023	9
2024	8
2025 and thereafter	68
Total lease payments	131
Capital leases
2020	3
2021	3
2022	3
2023	3
2024	2
2025 and thereafter	7
Total lease payments	21
Less: imputed interest	9
Total	$ 12

Commitments and Contingencies -

Commitments and Contingencies - Schedule of Raw Material Purchased under Long Term Purchase Agreements (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	$ 258	$ 466	$ 441
Reinforcement Materials [Member]
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	198	393	375
Performance Chemicals [Member]
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	58	65	55
Purification Solutions [Member]
Raw Material Purchased Under Long Term Purchase Agreements [Line Items]
Raw material purchased	$ 2	$ 8	$ 11

Commitments and Contingencies_2

Commitments and Contingencies - Additional Information (Detail) - USD ($)	3 Months Ended			12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Loss Contingencies [Line Items]
Raw material purchased				$ 258,000,000	$ 466,000,000	$ 441,000,000
Long term purchase commitment related to information technology				$ 14,000,000
Purchase agreement period				5 years
Charges for environmental expense				$ 1,000,000	1,000,000	6,000,000
Settlement amount				4,000,000	10,000,000	3,000,000
Respirator Liabilities [Member]
Loss Contingencies [Line Items]
Respirator reserve			$ 35,000,000	24,000,000	35,000,000
Respirator charge			20,000,000
Respirator liability				$ 65,200,000
Settlement amount	$ 32,600,000
Description of pending claims				The Company paid $32.6 million of this settlement in the third quarter of fiscal 2020.  The remaining $32.6 million is included in Accounts payable and accrued liabilities on the Consolidated Balance Sheets as of September 30, 2020 and was paid by the Company in the first quarter of fiscal 2021.
Respirator Liabilities [Member] | Accounts Payable and Accrued Liabilities [Member]
Loss Contingencies [Line Items]
Settlement amount				$ 32,600,000
Respirator Liabilities [Member] | Selling and Administrative Expenses [Member]
Loss Contingencies [Line Items]
Respirator charge				3,000,000
Respirator Liabilities [Member] | Selling and Administrative Expenses [Member]
Loss Contingencies [Line Items]
Respirator charge		$ 50,000,000			20,000,000	10,000,000
Environmental Matters [Member]
Loss Contingencies [Line Items]
Reserved for environmental matters			13,000,000	7,000,000	13,000,000
Reserve for environmental matters included in accrued expenses			9,000,000	3,000,000	9,000,000
Reserve for environmental matters included in other liabilities			4,000,000	4,000,000	4,000,000
Cash payments for environmental reserves				7,000,000	2,000,000	3,000,000
Environmental Matters [Member] | Operating and Maintenance Component [Member]
Loss Contingencies [Line Items]
Reserved for environmental matters				4,000,000
Per Accident for Auto [Member]
Loss Contingencies [Line Items]
Self-insured liability				500,000
Per Occurrence for All Other [Member]
Loss Contingencies [Line Items]
Self-insured liability				2,000,000
Per Accident for U.S. Workers' Compensation [Member]
Loss Contingencies [Line Items]
Self-insured liability				1,000,000
Maximum [Member]
Loss Contingencies [Line Items]
Retention for medical costs per person per annum				250,000
Charges related to value added tax matters				$ 30,000,000
Minimum [Member] | Respirator Liabilities [Member]
Loss Contingencies [Line Items]
Periods of pending claim				10 years
Non-Controlling Interests [Member]
Loss Contingencies [Line Items]
Raw material purchased				$ 81,000,000	156,000,000	$ 156,000,000
Accounts payable and accrued liabilities			$ 20,000,000	$ 12,000,000	$ 20,000,000

Commitments and Contingencies_3

Commitments and Contingencies - Schedule of Components of Purchase Commitments (Detail) $ in Millions	Sep. 30, 2020USD ($)
Long-term Purchase Commitment [Line Items]
Payments Due by Fiscal Year 2021	$ 169
Payments Due by Fiscal Year 2022	154
Payments Due by Fiscal Year 2023	121
Payments Due by Fiscal Year 2024	120
Payments Due by Fiscal Year 2025	121
Payments Due Thereafter	1,243
Payments Due, Total	1,928
Reinforcement Materials [Member]
Long-term Purchase Commitment [Line Items]
Payments Due by Fiscal Year 2021	115
Payments Due by Fiscal Year 2022	101
Payments Due by Fiscal Year 2023	87
Payments Due by Fiscal Year 2024	86
Payments Due by Fiscal Year 2025	86
Payments Due Thereafter	911
Payments Due, Total	1,386
Performance Chemicals [Member]
Long-term Purchase Commitment [Line Items]
Payments Due by Fiscal Year 2021	54
Payments Due by Fiscal Year 2022	53
Payments Due by Fiscal Year 2023	34
Payments Due by Fiscal Year 2024	34
Payments Due by Fiscal Year 2025	35
Payments Due Thereafter	332
Payments Due, Total	$ 542

Financial Information by Segm_3

Financial Information by Segment & Geographic Area - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Jun. 30, 2019Segment	Sep. 30, 2020SegmentBusiness_Unit
Segment Reporting Information [Line Items]
Number of business reportable segments	1	3
Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Number of business reportable segments		1
Number of business activity | Business_Unit		2

Financial Information by Segm_4

Financial Information by Segment & Geographic Area - Schedule of Performance Segment (Detail) - Performance Chemicals [Member] - Operating Segments [Member] - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Net sales	$ 933	$ 995	$ 1,028
Performance Additives [Member]
Segment Reporting Information [Line Items]
Net sales	645	694	707
Formulated Solutions [Member]
Segment Reporting Information [Line Items]
Net sales	$ 288	$ 301	$ 321

Financial Information by Segm_5

Financial Information by Segment & Geographic Area - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues from external customers	$ 659	$ 518	$ 710	$ 727	$ 827	$ 845	$ 844	$ 821	$ 2,614	$ 3,337	$ 3,242
Depreciation and amortization									158	148	149
Equity in earnings of affiliated companies									3	1	2
Income (loss) from continuing operations before income taxes									(33)	255	117
Assets	2,781				3,004				2,781	3,004	3,244
Total expenditures for additions to long-lived assets									169	247	229
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									2,442	3,144	3,126
Depreciation and amortization									156	147	152
Equity in earnings of affiliated companies									4	3	7
Income (loss) from continuing operations before income taxes									283	444	480
Assets	2,518				2,637				2,518	2,637	2,876
Total expenditures for additions to long-lived assets									166	242	224
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									172	193	116
Depreciation and amortization									2	1	(3)
Equity in earnings of affiliated companies									(1)	(2)	(5)
Income (loss) from continuing operations before income taxes									(316)	(189)	(363)
Assets	263				367				263	367	368
Total expenditures for additions to long-lived assets									3	5	5
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									1,256	1,815	1,774
Depreciation and amortization									68	69	70
Equity in earnings of affiliated companies										(1)	1
Income (loss) from continuing operations before income taxes									162	266	279
Assets	1,077				1,177				1,077	1,177	1,319
Total expenditures for additions to long-lived assets									66	82	97
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									933	995	1,028
Depreciation and amortization									64	51	48
Equity in earnings of affiliated companies									1	1
Income (loss) from continuing operations before income taxes									118	152	200
Assets	1,145				1,024				1,145	1,024	919
Total expenditures for additions to long-lived assets									92	148	94
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									253	278	279
Depreciation and amortization									24	26	32
Equity in earnings of affiliated companies									3	3	6
Income (loss) from continuing operations before income taxes									3	2	(7)
Assets	$ 296				$ 436				296	436	460
Total expenditures for additions to long-lived assets									$ 8	11	16
Specialty Fluids [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers										56	45
Depreciation and amortization										1	2
Income (loss) from continuing operations before income taxes										24	8
Assets											178
Total expenditures for additions to long-lived assets										$ 1	$ 17

Financial Information by Segm_6

Financial Information by Segment & Geographic Area - Financial Information by Reportable Segment (Parenthetical) (Detail)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting [Abstract]
Percentage of sale of an equity method affiliate	100.00%	100.00%	100.00%

Financial Information by Segm_7

Financial Information by Segment & Geographic Area - Sales of Equity Method Affiliate and Discounting Charges for Certain Notes Receivable (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenues from external customers	$ 659	$ 518	$ 710	$ 727	$ 827	$ 845	$ 844	$ 821	$ 2,614	$ 3,337	$ 3,242
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									172	193	116
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									(3)	(13)	11
Unallocated and Other [Member] | Shipping and Handling Costs [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									113	130	$ 105
Unallocated and Other [Member] | By-product Sales [Member]
Segment Reporting Information [Line Items]
Revenues from external customers									$ 62	$ 76

Financial Information by Segm_8

Financial Information by Segment & Geographic Area - Sales of Equity Method Affiliate and Discounting Charges for Certain Notes Receivable (Parenthetical) (Detail)	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting [Abstract]
Percentage of sale of an equity method affiliate	100.00%	100.00%	100.00%

Financial Information by Segm_9

Financial Information by Segment & Geographic Area - Schedule of Income (Loss) from Continuing Operations before Income Taxes and Equity in Earnings of Affiliated Companies for Unallocated and Other (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Interest expense		$ (53)	$ (59)	$ (54)
Global restructuring activities		(19)	(16)	30
Gains (losses) on sale of investments				10
Purification Solutions [Member]
Segment Reporting Information [Line Items]
Goodwill and long-lived assets impairment charge	$ (224)
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Interest expense		(53)	(59)	(54)
Unallocated corporate costs		(41)	(50)	(61)
General unallocated income (expense)		(1)	8	2
Less: Equity in earnings of affiliated companies, net of tax		3	1	2
Income from continuing operations before income taxes and equity in earnings of affiliated companies		(316)	(189)	(363)
Certain Items [Member]
Segment Reporting Information [Line Items]
Legal and environmental matters and reserves		(54)	(21)	(16)
Global restructuring activities		(19)	(16)	30
Employee benefit plan settlement and other charges		(10)	1
Acquisition and integration-related charges		(5)	(6)	(2)
Inventory reserve adjustment		(2)		(13)
Executive transition costs			(1)	(2)
Indirect tax settlement credits		3
Gains (losses) on sale of investments				10
Other certain items		(1)	(4)	(1)
Total certain items, pre-tax		(218)	(87)	(248)
Certain Items [Member] | Marshall Mine [Member]
Segment Reporting Information [Line Items]
Loss on sale and asset impairment charge		(129)
Certain Items [Member] | Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Loss on sale and asset impairment charge		$ (1)	(29)
Certain Items [Member] | Equity Affiliate Investment [Member]
Segment Reporting Information [Line Items]
Investment impairment charge			$ (11)
Certain Items [Member] | Purification Solutions [Member]
Segment Reporting Information [Line Items]
Goodwill and long-lived assets impairment charge				$ (254)

Financial Information by Seg_10

Financial Information by Segment & Geographic Area - Revenue from External Customers and Long-Lived Asset Information by Geographic Area (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues from external customers	$ 659	$ 518	$ 710	$ 727	$ 827	$ 845	$ 844	$ 821	$ 2,614	$ 3,337	$ 3,242
Net property, plant and equipment	1,314				1,348				1,314	1,348	1,296
United States [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues from external customers									581	702	676
Net property, plant and equipment	493				572				493	572	493
China [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues from external customers									598	738	752
Net property, plant and equipment	295				264				295	264	270
Other Countries [Member]
Revenues From External Customers And Long Lived Assets [Line Items]
Revenues from external customers									1,435	1,897	1,814
Net property, plant and equipment	$ 526				$ 512				$ 526	$ 512	$ 533

Financial Information by Seg_11

Financial Information by Segment & Geographic Area - Revenue from External Customers by Geographic Region (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 659	$ 518	$ 710	$ 727	$ 827	$ 845	$ 844	$ 821	$ 2,614	$ 3,337	$ 3,242
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									2,442	3,144	3,126
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									172	193	116
Reinforcement Materials [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									1,256	1,815	1,774
Performance Chemicals [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									933	995	1,028
Purification Solutions [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									253	278	279
Specialty Fluids [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues										56	$ 45
Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									868	1,114
Americas [Member] | Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									490	688
Americas [Member] | Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									266	294
Americas [Member] | Purification Solutions [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									112	126
Americas [Member] | Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues										6
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									931	1,158
Asia Pacific [Member] | Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									529	769
Asia Pacific [Member] | Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									368	353
Asia Pacific [Member] | Purification Solutions [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									34	35
Asia Pacific [Member] | Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues										1
Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									643	872
Europe, Middle East and Africa [Member] | Reinforcement Materials [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									237	358
Europe, Middle East and Africa [Member] | Performance Chemicals [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									299	348
Europe, Middle East and Africa [Member] | Purification Solutions [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues									$ 107	117
Europe, Middle East and Africa [Member] | Specialty Fluids [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues										$ 49

Unaudited Quarterly Financial_3

Unaudited Quarterly Financial Information - Schedule of Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Quarterly Financial Information Disclosure [Abstract]
Net sales and other operating revenues	$ 659	$ 518	$ 710	$ 727	$ 827	$ 845	$ 844	$ 821	$ 2,614	$ 3,337	$ 3,242
Gross profit	137	69	153	141	171	170	178	166	500	685	772
Net income (loss)	(265)	(5)	3	46	40	40	29	77	(221)	186	(74)
Net income (loss) attributable to Cabot Corporation	$ (272)	$ (6)	$ (1)	$ 41	$ 33	$ 32	$ 23	$ 69	$ (238)	$ 157	$ (113)
Earnings per common share—basic	$ (4.81)	$ (0.12)	$ (0.01)	$ 0.71	$ 0.56	$ 0.55	$ 0.39	$ 1.14	$ (4.21)	$ 2.64	$ (1.85)
Earnings per common share—diluted	$ (4.81)	$ (0.12)	$ (0.01)	$ 0.70	$ 0.55	$ 0.55	$ 0.39	$ 1.14	$ (4.21)	$ 2.63	$ (1.85)

Unaudited Quarterly Financial_4

Unaudited Quarterly Financial Information - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020
Respirator Liabilities [Member]
Schedule Of Quarterly Financial Information Disclosure [Line Items]
Respirator charge		$ 20
U.S. Defined Benefit Plans [Member]
Schedule Of Quarterly Financial Information Disclosure [Line Items]
Net deferred tax asset carge due to a valuation allowance increase	$ 228		$ 228
Marshall Mine [Member]
Schedule Of Quarterly Financial Information Disclosure [Line Items]
Loss on sale and asset impairment charge	$ 129		$ 129