Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Millions	Total	Common Stock, Net of Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total Cabot Corporation Stockholders' Equity [Member]	Noncontrolling Interests [Member]
Beginning Balance at Sep. 30, 2021	$ 1,090	$ 53	$ 24	$ 1,159	$ (289)	$ 947	$ 143
Beginning Balance, Shares at Sep. 30, 2021		56,727
Net income (loss)	(80)			(89)		(89)	9
Total other comprehensive income (loss)	(28)				(30)	(30)	2
Cash dividends paid, Common stock, per share	(21)			(21)		(21)
Issuance of stock under equity compensation plans, Shares		202
Share-based compensation	6		6			6
Purchase and retirement of common stock	(19)		(19)			(19)
Purchase and retirement of common stock, Shares		(349)
Ending Balance at Dec. 31, 2021	948	$ 53	11	1,049	(319)	794	154
Ending Balance, Shares at Dec. 31, 2021		56,580
Beginning Balance at Sep. 30, 2022	1,032	$ 52	1	1,284	(439)	898	134
Beginning Balance, Shares at Sep. 30, 2022		56,249
Net income (loss)	66			54		54	12
Total other comprehensive income (loss)	87				81	81	6
Cash dividends paid, Common stock, per share	(21)			(21)		(21)
Cash dividends declared to noncontrolling interests	(2)						(2)
Issuance of stock under equity compensation plans	3	$ 1	2			3
Issuance of stock under equity compensation plans, Shares		309
Share-based compensation	11		11			11
Purchase and retirement of common stock	(17)		$ (14)	(3)		(17)
Purchase and retirement of common stock, Shares		(242)
Ending Balance at Dec. 31, 2022	$ 1,159	$ 53		$ 1,314	$ (358)	$ 1,009	$ 150
Ending Balance, Shares at Dec. 31, 2022		56,316