Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Income Statement [Abstract]
Net sales and other operating revenues	$ 955	$ 958
Cost of sales	720	740
Gross profit	235	218
Selling and administrative expenses	66	67
Research and technical expenses	14	15
Income (loss) from operations	155	136
Interest and dividend income	6	9
Interest expense	(18)	(22)
Other income (expense)	1	(29)
Income (loss) from operations before income taxes and equity in earnings of affiliated companies	144	94
(Provision) benefit for income taxes	(41)	(34)
Equity in earnings of affiliated companies, net of tax	1	1
Net income (loss)	104	61
Net income (loss) attributable to noncontrolling interests, net of tax	11	11
Net income (loss) attributable to Cabot Corporation	$ 93	$ 50
Weighted-average common shares outstanding:
Basic	54.3	55.3
Diluted	55.0	55.8
Earnings (loss) per common share:
Basic	$ 1.69	$ 0.88
Diluted	$ 1.67	$ 0.88