Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 114	$ 85	$ 34	$ 155
Other comprehensive income (loss), net of tax
Foreign currency translation adjustment, net of tax	46	(76)	18	18
Derivatives: net investment hedges
(Gains) losses reclassified to interest expense, net of tax	(2)	(2)	(3)	(3)
(Gains) losses excluded from effectiveness testing and amortized to interest expense, net of tax	1	1	1	1
Pension and other postretirement benefit liability adjustments, net of tax	1	1	2	4
Other comprehensive income (loss), net of tax of $‒, $‒, $(1), and $(3)	46	(76)	18	20
Comprehensive income (loss)	160	9	52	175
Net income (loss) attributable to noncontrolling interests, net of tax	7	10	16	20
Foreign currency translation adjustment attributable to noncontrolling interests, net of tax	1	(2)	3	5
Comprehensive income (loss) attributable to noncontrolling interests	8	8	19	25
Comprehensive income (loss) attributable to Cabot Corporation	$ 152	$ 1	$ 33	$ 150