Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Net sales and other operating revenues	$ 3,409	$ 2,614	$ 3,337
Cost of sales	2,610	2,114	2,652
Gross profit	799	500	685
Selling and administrative expenses	289	292	290
Research and technical expenses	56	57	60
Income (loss) from operations	454	21	306
Interest and dividend income	8	8	9
Interest expense	(49)	(53)	(59)
Other income (expense)	(7)	(9)	(1)
Income (loss) from continuing operations before income taxes and equity in earnings of affiliated companies	406	(33)	255
(Provision) benefit for income taxes	(123)	(191)	(70)
Equity in earnings of affiliated companies, net of tax	3	3	1
Net income (loss)	286	(221)	186
Net income (loss) attributable to noncontrolling interests, net of tax of $10, $4 and $6	36	17	29
Net income (loss) attributable to Cabot Corporation	$ 250	$ (238)	$ 157
Weighted-average common shares outstanding:
Basic	56.7	56.6	58.7
Diluted	56.8	56.6	58.8
Earnings (loss) per common share:
Basic	$ 4.35	$ (4.21)	$ 2.64
Diluted	$ 4.34	$ (4.21)	$ 2.63
Specialty Fluids [Member]
Loss on sale and asset impairment charge		$ 1	$ 29
Marshall Mine [Member]
Loss on sale and asset impairment charge		$ 129