Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021
Income Statement [Abstract]
Net sales and other operating revenues	$ 1,092	$ 842	$ 2,060	$ 1,588
Cost of sales	860	628	1,630	1,181
Gross profit	232	214	430	407
Selling and administrative expenses	74	71	145	132
Research and technical expenses	14	15	27	29
Loss on sale of business and asset impairment charge (Note D)	7		204
Gain on bargain purchase of a business (Note C)	(24)		(24)
Income (loss) from operations	161	128	78	246
Interest and dividend income	4	2	7	4
Interest expense	(11)	(13)	(23)	(25)
Other income (expense)	(7)	1	(8)	(8)
Income (loss) before income taxes and equity in earnings of affiliated companies	147	118	54	217
(Provision) benefit for income taxes	(36)	(34)	(24)	(63)
Equity in earnings of affiliated companies, net of tax	3	1	4	1
Net income (loss)	114	85	34	155
Net income (loss) attributable to noncontrolling interests, net of tax	7	10	16	20
Net income (loss) attributable to Cabot Corporation	$ 107	$ 75	$ 18	$ 135
Weighted-average common shares outstanding:
Basic	56.6	56.6	56.5	56.6
Diluted	57.1	56.7	56.9	56.7
Earnings (loss) per common share:
Basic	$ 1.86	$ 1.31	$ 0.30	$ 2.37
Diluted	$ 1.84	$ 1.30	$ 0.30	$ 2.36