Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 120	$ 90	$ 278	$ 238
Other comprehensive income (loss), net of tax
Foreign currency translation adjustment, net of tax	(66)	(20)	(19)	117
Derivatives: net investment hedges
(Gains) losses reclassified to interest expense, net of tax	(1)	(1)	(3)	(4)
(Gains) losses excluded from effectiveness testing and amortized to interest expense, net of tax	1		2	1
Pension and other post-retirement benefit liability adjustments, net of tax			(1)	(1)
Other comprehensive income (loss), net of tax (provision) benefit of $ (1), $ -, $ 11 and $ -	(66)	(21)	(21)	113
Comprehensive income (loss)	54	69	257	351
Net income (loss) attributable to noncontrolling interests, net of tax	11	8	35	27
Foreign currency translation adjustment attributable to noncontrolling interests, net of tax	(1)	(6)	(1)	3
Comprehensive income (loss) attributable to noncontrolling interests	10	2	34	30
Comprehensive income (loss) attributable to Cabot Corporation	$ 44	$ 67	$ 223	$ 321