Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 61	$ 66
Other comprehensive income (loss), net of tax
Foreign currency translation adjustment, net of tax	62	88
Derivatives: net investment hedges
(Gains) losses reclassified to interest expense, net of tax	(1)	(1)
Other comprehensive income (loss), net of tax of $ 1 and $ -	61	87
Comprehensive income (loss)	122	153
Net income (loss) attributable to noncontrolling interests, net of tax	11	12
Foreign currency translation adjustment attributable to noncontrolling interests, net of tax	4	6
Comprehensive income (loss) attributable to noncontrolling interests	15	18
Comprehensive income (loss) attributable to Cabot Corporation	$ 107	$ 135