Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Income Statement [Abstract]
Net sales and other operating revenues	$ 923	$ 1,016	$ 2,814	$ 2,993
Cost of sales	679	760	2,094	2,273
Gross profit	244	256	720	720
Selling and administrative expenses	62	68	192	210
Research and technical expenses	15	16	44	46
Income (loss) from operations	167	172	484	464
Interest and dividend income	7	8	20	25
Interest expense	(19)	(19)	(56)	(62)
Other income (expense)		(3)	2	(33)
Income (loss) from operations before income taxes and equity in earnings of affiliated companies	155	158	450	394
(Provision) benefit for income taxes	(43)	(40)	(133)	(121)
Equity in earnings of affiliated companies, net of tax	1	2	5	5
Net income (loss)	113	120	322	278
Net income (loss) attributable to noncontrolling interests, net of tax	12	11	34	35
Net income (loss) attributable to Cabot Corporation	$ 101	$ 109	$ 288	$ 243
Weighted-average common shares outstanding:
Basic	53.5	55.1	53.9	55.3
Diluted	53.8	55.7	54.4	55.8
Earnings (loss) per common share:
Basic	$ 1.87	$ 1.96	$ 5.27	$ 4.34
Diluted	$ 1.86	$ 1.94	$ 5.22	$ 4.3