Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 97	$ 82	$ 158	$ 148
Other comprehensive income (loss), net of tax
Foreign currency translation adjustment, net of tax	(15)	49	47	137
Derivatives: net investment hedges
(Gains) losses reclassified to interest expense, net of tax	(1)	(2)	(2)	(3)
(Gains) losses excluded from effectiveness testing and amortized to interest expense, net of tax	1	1	1	1
Pension and other post-retirement benefit liability adjustments, net of tax	(1)	(1)	(1)	(1)
Other comprehensive income (loss), net of tax (provision) benefit of $ 11, $ -,$ 12 and $ -	(16)	47	45	134
Comprehensive income (loss)	81	129	203	282
Net income (loss) attributable to noncontrolling interests, net of tax	13	7	24	19
Foreign currency translation adjustment attributable to noncontrolling interests, net of tax	(4)	3		9
Comprehensive income (loss) attributable to noncontrolling interests	9	10	24	28
Comprehensive income (loss) attributable to Cabot Corporation	$ 72	$ 119	$ 179	$ 254