Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Income Statement [Abstract]
Net sales and other operating revenues	$ 1,016	$ 968	$ 2,993	$ 2,966
Cost of sales	760	745	2,273	2,352
Gross profit	256	223	720	614
Selling and administrative expenses	68	58	210	184
Research and technical expenses	16	15	46	43
Loss on sale of business				3
Income (loss) from operations	172	150	464	384
Interest and dividend income	8	7	25	22
Interest expense	(19)	(24)	(62)	(69)
Other income (expense)	(3)	(3)	(33)	(13)
Income (loss) from operations before income taxes and equity in earnings of affiliated companies	158	130	394	324
(Provision) benefit for income taxes	(40)	(41)	(121)	(90)
Equity in earnings of affiliated companies, net of tax	2	1	5	4
Net income (loss)	120	90	278	238
Net income (loss) attributable to noncontrolling interests, net of tax	11	8	35	27
Net income (loss) attributable to Cabot Corporation	$ 109	$ 82	$ 243	$ 211
Weighted-average common shares outstanding:
Basic	55.1	56.1	55.3	56.2
Diluted	55.7	56.5	55.8	56.7
Earnings (loss) per common share:
Basic	$ 1.96	$ 1.44	$ 4.34	$ 3.68
Diluted	$ 1.94	$ 1.43	$ 4.3	$ 3.65