Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Income Statement [Abstract]
Net sales and other operating revenues	$ 968	$ 746
Cost of sales	770	553
Gross profit	198	193
Selling and administrative expenses	71	61
Research and technical expenses	13	14
Purification Solutions assets held for sale impairment charge (Note D)	197
Income (loss) from operations	(83)	118
Interest and dividend income	3	2
Interest expense	(12)	(12)
Other income (expense)	(1)	(9)
Income (loss) before income taxes and equity in earnings of affiliated companies	(93)	99
(Provision) benefit for income taxes	12	(29)
Equity in earnings of affiliated companies, net of tax	1	0
Net income (loss)	(80)	70
Net income (loss) attributable to noncontrolling interests, net of tax	9	10
Net income (loss) attributable to Cabot Corporation	$ (89)	$ 60
Weighted-average common shares outstanding:
Basic	56.8	56.5
Diluted	56.8	56.6
Earnings (loss) per common share:
Basic	$ (1.57)	$ 1.06
Diluted	$ (1.57)	$ 1.06