Earnings Per Share - Calculation of Undistributed Earnings (Detail) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Earnings Per Share [Abstract]
Net income (loss) attributable to Cabot Corporation	$ 54	$ (89)
Less: Dividends declared on common stock	21	21
Undistributed earnings (loss)	33	(110)
Undistributed earnings (loss) allocated to common shareholders	32	$ (110)
Undistributed earnings allocated to participating shareholders	$ 1