Employee Benefit Plans (Tables)

12 Months Ended

Sep. 30, 2023

Retirement Benefits [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
	2023					2022						2023						2022
	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	$	2	$	133		$	3		$	221		$	16		$	13		$	25		$	19
Service cost		—		3			—			4			—			—			—			—
Interest cost		—		7			—			4			1			1			—			1
Plan participants’ contribution		—		1			—			1			—			—			—			—
Foreign currency exchange rate    changes		—		6			—			(27	)		—			1			—			(2	)
(Gain) loss from changes in actuarial    assumptions and plan experience		—		(4	)		(1	)		(43	)		(1	)		(3	)		(4	)		(5	)
Benefits paid		—		(5	)		—			(9	)		(2	)		(1	)		(3	)		—
Settlements or curtailments		—		(2	)		—			(2	)		—			—			(2	)		—
Divestiture of a business		—		—			—			(16	)		—			—			—			—
Benefit obligation at end of year	$	2	$	139		$	2		$	133		$	14		$	11		$	16		$	13

	Years Ended September 30
	2023						2022						2023						2022
	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	$	—		$	135		$	—		$	217		$	—		$	—		$	—		$	—
Actual return on plan assets		—			4			—			(35	)		—			—			—			—
Employer contribution		—			4			—			5			2			1			5			—
Plan participants’ contribution		—			1			—			1			—			—			—			—
Foreign currency exchange rate    changes		—			7			—			(24	)		—			—			—			—
Benefits paid		—			(5	)		—			(9	)		(2	)		(1	)		(3	)		—
Settlements or curtailments		—			(2	)		—			(2	)		—			—			(2	)		—
Expenses paid from assets		—			—			—			—			—			—			—			—
Divestiture of a business		—			—			—			(18	)		—			—			—			—
Fair value of plan assets at end    of year	$	—		$	144		$	—		$	135		$	—		$	—		$	—		$	—
Funded status	$	(2	)	$	5		$	(2	)	$	2		$	(14	)	$	(11	)	$	(16	)	$	(13	)
Recognized asset (liability)	$	(2	)	$	5		$	(2	)	$	2		$	(14	)	$	(11	)	$	(16	)	$	(13	)

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:

	2023						2022						2021
	Pension Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign
Actuarial assumptions as of the year-end    measurement date:
Discount rate		6.0	%		4.7	%		5.5	%		4.5	%		2.2	%		2.1	%
Rate of increase in compensation	N/A				3.0	%		3.0	%		3.0	%	N/A				2.9	%
Cash balance interest credit rate		2.0	%		2.1	%		2.0	%		2.0	%		2.0	%		1.7	%
Actuarial assumptions used to determine net    periodic benefit cost during the year:
Discount rate - benefit obligation		5.6	%		4.5	%		2.2	%		2.1	%		2.5	%		1.7	%
Discount rate - service cost	N/A				3.6	%	N/A				2.0	%	N/A				1.7	%
Discount rate - interest cost		5.3	%		4.5	%		1.6	%		1.7	%		1.4	%		1.4	%
Expected long-term rate of return on    plan assets	N/A				5.1	%	N/A				3.5	%	N/A				4.6	%
Rate of increase in compensation	N/A				3.0	%	N/A				2.9	%	N/A				3.0	%
Cash balance interest credit rate		2.0	%		2.0	%		2.0	%		1.7	%		2.1	%		1.7	%

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:

	2023						2022						2021
	Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign
Actuarial assumptions as of the year-end    measurement date:
Discount rate		6.0	%		5.7	%		5.6	%		5.1	%		2.4	%		2.8	%
Initial health care cost trend rate(1)		5.0	%		6.4	%		—	%		6.8	%		5.5	%		6.9	%
Actuarial assumptions used to determine    net cost during the year:
Discount rate - benefit obligation		5.6	%		5.1	%		2.4	%		2.8	%		2.1	%		2.4	%
Discount rate - service cost		5.4	%		5.1	%		1.7	%		3.5	%		1.5	%		3.0	%
Discount rate - interest cost		5.3	%		5.1	%		1.6	%		2.5	%		1.4	%		2.1	%
Initial health care cost trend rate(1)		—	%		6.8	%		5.5	%		6.9	%		6.0	%		6.9	%

(1)The initial health care cost trend rate is set at 5% for the 2023 U.S. plan assumptions as the 2024 Medicare Part B premiums are expected to increase. The trend rates for all future years beyond 2024 also reflect expected 5% increases. The initial health care cost trend rate was set at zero for the 2022 U.S. plan assumptions in light of the expected downward adjustment the U.S. government was expected to make to the 2023 Medicare Part B premiums, however, all trend rates beyond the initial year were set to 5%.

Amounts Recognized in Consolidated Balance Sheets

Amounts recognized in the Consolidated Balance Sheets at September 30, 2023 and 2022 related to the Company's defined benefit pension and postretirement benefit plans were as follows:

	September 30
	2023						2022						2023						2022
	Pension Benefits												Postretirement Benefits
	U.S.			Foreign			U.S.			Foreign			U.S.			Foreign			U.S.			Foreign
	(In millions)
Other assets	$	—		$	30		$	—		$	26		$	—		$	—		$	—		$	—
Accounts payable and accrued liabilities	$	—		$	(1	)	$	—		$	(1	)	$	(2	)	$	(1	)	$	(2	)	$	(1	)
Other liabilities	$	(2	)	$	(24	)	$	(2	)	$	(23	)	$	(12	)	$	(10	)	$	(14	)	$	(12	)

Amounts Recognized in AOCI

Amounts recognized in AOCI at September 30, 2023 and 2022 related to the Company's defined benefit pension and postretirement benefit plans were as follows:

	September 30
	2023					2022					2023						2022
	Pension Benefits										Postretirement Benefits
	U.S.		Foreign			U.S.		Foreign			U.S.			Foreign			U.S.			Foreign
	(In millions)
Net actuarial (gain) loss	$	—	$	24		$	—	$	23		$	(6	)	$	(7	)	$	(6	)	$	(4	)
Net prior service credit		—		(1	)		—		(1	)		—			—			—			—
Balance in accumulated other    comprehensive (income) loss, pretax	$	—	$	23		$	—	$	22		$	(6	)	$	(7	)	$	(6	)	$	(4	)

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 2024 to 2033:

	Pension Benefits				Postretirement Benefits
Years Ending September 30	U.S.		Foreign		U.S.		Foreign
	(In millions)
2024	$	—	$	9	$	2	$	1
2025	$	—	$	9	$	2	$	1
2026	$	—	$	9	$	2	$	1
2027	$	—	$	11	$	2	$	1
2028	$	—	$	11	$	2	$	1
2029 - 2033	$	1	$	49	$	6	$	4

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
	2023					2022					2021					2023					2022					2021
	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	$	—	$	3		$	—	$	4		$	—	$	6		$	—		$	—	$	—		$	—	$	—	$	—
Interest cost		—		7			—		4			—		3			1			1		—			1		—		1
Expected return on plan    assets		—		(7	)		—		(6	)		—		(10	)		—			—		—			—		—		—
Amortization of net losses		—		(1	)		—		1			—		3			(1	)		—		—			—		—		—
Settlements or    Curtailments cost		—		—			—		—			4		1			—			—		(1	)		—		—		—
Other		—		—			—		—			—		2			—			—		—			—		—		—
Net periodic (benefit) cost	$	—	$	2		$	—	$	3		$	4	$	5		$	—		$	1	$	(1	)	$	1	$	—	$	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
	2023				2022					2021						2023						2022						2021
	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	$	—	$	1	$	—	$	(2	)	$	(2	)	$	(15	)	$	(1	)	$	(3	)	$	(4	)	$	(4	)	$	—	$	(2	)
Prior service (credit) cost		—		—		—		—			—			(1	)					—			—			—			—		—
Amortization of prior    unrecognized loss		—		1		—		(1	)		—			(3	)		1			—			—			—			—		—
Loss on divestiture		—		—		—		(2	)		—			—			—			—			—			—			—		—
(Loss) gain on settlements		—		—		—		—			(4	)		(1	)		—			—			1			—			—		—
Net changes recognized in    Total other comprehensive    (income) loss (1)	$	—	$	2	$	—	$	(5	)	$	(6	)	$	(20	)	$	—		$	(3	)	$	(3	)	$	(4	)	$	—	$	(2	)

(1)The tax impact on pension and other postretirement benefit liability adjustments arising during the period was a tax provision of less than $1 million, a tax benefit of $3 million and a tax benefit of $8 million for fiscal 2023, 2022 and 2021, respectively.

Defined Benefit Pension Plans Weighted-Average Asset Allocations

The Company’s foreign defined benefit pension plans weighted-average asset allocations at September 30, 2023 and 2022 by asset category, are as follows:

	September 30
	2023			2022
Equity securities		19	%		20	%
Debt securities		31	%		68	%
Real estate		10	%		7	%
Cash and other securities (1)		40	%		5	%
Total		100	%		100	%

(1)The asset allocation is temporarily changed as a result of the insurance contracts Cabot Carbon Limited Pension Plan and Carbon Plastics Pension Plan purchased with plan assets in anticipation of the settlement discussed above.

Fair Value of Pension Plan Assets by Asset Category

The fair value of the Company’s pension plan assets at September 30, 2023 and 2022 by asset category is as follows:

	September 30
	2023						2022
	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	$	—	$	—	$	—	$	1	$	—	$	1
Direct investments:
U.S government bonds		—		—		—		—		—		—
U.S. corporate bonds		—		—		—		—		—		—
Non-U.S. equities		6		—		6		4		—		4
Non-U.S. government bonds		2		—		2		1		—		1
Non-U.S. corporate bonds		3		—		3		2		—		2
Mortgage-backed securities		—		1		1		—		1		1
Other fixed income		1		—		1		1		—		1
Total direct investments		12		1		13		8		1		9
Investment funds:
Equity funds(1)		—		21		21		—		23		23
Fixed income funds(2)		—		38		38		—		86		86
Real estate funds(3)		—		15		15		—		9		9
Cash equivalent funds		4		—		4		1		—		1
Other investment funds		—		—		—		—		1		1
Total investment funds		4		74		78		1		119		120
Alternative investments:
Insurance contracts(4)		—		52		52		—		5		5
Other alternative investments		—		1		1		—		—		—
Total alternative investments		—		53		53		—		5		5
Total pension plan assets	$	16	$	128	$	144	$	10	$	125	$	135

(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.