Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Income Statement [Abstract]
Net sales and other operating revenues	$ 1,019	$ 1,033	$ 1,977	$ 1,998
Cost of sales	773	823	1,513	1,607
Gross profit	246	210	464	391
Selling and administrative expenses	75	66	142	126
Research and technical expenses	15	15	30	28
Loss on sale of business				3
Income (loss) from operations	156	129	292	234
Interest and dividend income	8	9	17	15
Interest expense	(21)	(23)	(43)	(45)
Other income (expense)	(1)	(5)	(30)	(10)
Income (loss) from operations before income taxes and equity in earnings of affiliated companies	142	110	236	194
(Provision) benefit for income taxes	(47)	(29)	(81)	(49)
Equity in earnings of affiliated companies, net of tax	2	1	3	3
Net income (loss)	97	82	158	148
Net income (loss) attributable to noncontrolling interests, net of tax	13	7	24	19
Net income (loss) attributable to Cabot Corporation	$ 84	$ 75	$ 134	$ 129
Weighted-average common shares outstanding:
Basic	55.4	56.3	55.3	56.3
Diluted	55.8	56.8	55.8	56.7
Earnings (loss) per common share:
Basic	$ 1.5	$ 1.31	$ 2.39	$ 2.24
Diluted	$ 1.49	$ 1.29	$ 2.37	$ 2.23