Accumulated Other Comprehensive Income (Loss) ("AOCI") (Tables)

9 Months Ended

Jun. 30, 2025

Equity [Abstract]

Changes in Each Component of AOCI, Net of Tax

Changes in each component of AOCI, net of tax, were as follows:

	Currency Translation Adjustment			Pension and Other Post-retirement Benefit Liability Adjustments			Total
	(In millions)
Balance at September 30, 2024, attributable to Cabot Corporation	$	(342	)	$	(18	)	$	(360	)
Other comprehensive income (loss) before reclassifications		(104	)		—			(104	)
Amounts reclassified from AOCI		—			—			—
Less: Other comprehensive income (loss) attributable to    noncontrolling interests		(7	)		—			(7	)
Balance at December 31, 2024, attributable to Cabot Corporation	$	(439	)	$	(18	)	$	(457	)
Other comprehensive income (loss) before reclassifications		34			1			35
Amounts reclassified from AOCI		(1	)		(1	)		(2	)
Less: Other comprehensive income (loss) attributable to    noncontrolling interests		3			—			3
Balance at March 31, 2025, attributable to Cabot Corporation	$	(409	)	$	(18	)	$	(427	)
Other comprehensive income (loss) before reclassifications		76			—			76
Amounts reclassified from AOCI		—			—			—
Less: Other comprehensive income (loss) attributable to    noncontrolling interests		4			—			4
Balance at June 30, 2025, attributable to Cabot Corporation	$	(337	)	$	(18	)	$	(355	)

	Currency Translation Adjustment			Pension and Other Post-retirement Benefit Liability Adjustments			Total
	(In millions)
Balance at September 30, 2023, attributable to Cabot Corporation	$	(353	)	$	(9	)	$	(362	)
Other comprehensive income (loss) before reclassifications		62			—			62
Amounts reclassified from AOCI		(1	)		—			(1	)
Less: Other comprehensive income (loss) attributable to    noncontrolling interests		4			—			4
Balance at December 31, 2023, attributable to Cabot Corporation	$	(296	)	$	(9	)	$	(305	)
Other comprehensive income (loss) before reclassifications		(15	)		—			(15	)
Amounts reclassified from AOCI		—			(1	)		(1	)
Less: Other comprehensive income (loss) attributable to    noncontrolling interests		(4	)		—			(4	)
Balance at March 31, 2024, attributable to Cabot Corporation	$	(307	)	$	(10	)	$	(317	)
Other comprehensive income (loss) before reclassifications		(66	)		—			(66	)
Amounts reclassified from AOCI		—			—			—
Less: Other comprehensive income (loss) attributable to    noncontrolling interests		(1	)		—			(1	)
Balance at June 30, 2024, attributable to Cabot Corporation	$	(372	)	$	(10	)	$	(382	)

Amounts Reclassified Out of AOCI

The amounts reclassified out of AOCI and into the Consolidated Statements of Operations in each of the three and nine months ended June 30, 2025 and 2024 are as follows:

	Affected Line Item in the Consolidated	Three Months Ended June 30						Nine Months Ended June 30
	Statements of Operations	2025			2024			2025			2024
		(In millions)
Derivatives: net investment hedges
(Gains) losses reclassified to interest    expense	Interest expense	$	(1	)	$	(1	)	$	(4	)	$	(4	)
(Gains) losses excluded from effectiveness testing and amortized to interest expense	Interest expense		1			1			2			2
Pension and other postretirement
Amortization of actuarial losses and prior service cost (credit)	Other income (expense)		—			—			(1	)		(1	)
Total before tax		$	—		$	—		$	(3	)	$	(3	)