Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Net sales and other operating revenues	$ 603	$ 812
Cost of sales	504	655
Gross profit	99	157
Selling and administrative expenses	71	78
Research and technical expenses	16	15
Income from operations	12	64
Interest and dividend income	1	1
Interest expense	(13)	(13)
Other expense	(8)	(1)
(Loss) income from continuing operations	(8)	51
Benefit (provision) for income taxes	5	(3)
Equity in earnings of affiliated companies, net of tax		1
Net (loss) income	(3)	49
Net income attributable to noncontrolling interests, net of tax	4	4
Net (loss) income attributable to Cabot Corporation	$ (7)	$ 45
Weighted-average common shares outstanding, in millions:
Basic	62.5	64.1
Diluted	62.5	64.6
Basic:
Net (loss) income attributable to Cabot Corporation	$ (0.11)	$ 0.70
Diluted:
Net (loss) income attributable to Cabot Corporation	(0.11)	0.69
Dividends per common share	$ 0.22	$ 0.22