Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Net sales and other operating revenues	$ 746	$ 727
Cost of sales	553	586
Gross profit	193	141
Selling and administrative expenses	61	64
Research and technical expenses	14	14
Income (loss) from operations	118	63
Interest and dividend income	2	3
Interest expense	(12)	(14)
Other income (expense)	(9)	(2)
Income (loss) before income taxes and equity in earnings of affiliated companies	99	50
(Provision) benefit for income taxes	(29)	(4)
Net income (loss)	70	46
Net income (loss) attributable to noncontrolling interests, net of tax	10	5
Net income (loss) attributable to Cabot Corporation	$ 60	$ 41
Weighted-average common shares outstanding:
Basic	56.5	56.9
Diluted	56.6	57.0
Earnings (loss) per common share:
Basic	$ 1.06	$ 0.71
Diluted	$ 1.06	$ 0.70