Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Net sales and other operating revenues	$ 854	$ 705	$ 2,392	$ 1,994
Cost of sales	654	544	1,824	1,505
Gross profit	200	161	568	489
Selling and administrative expenses	74	63	221	191
Research and technical expenses	17	14	48	40
Long-lived assets impairment (Note E)			162
Goodwill impairment (Note E)			92
Income (loss) from operations	109	84	45	258
Interest and dividend income	2	3	8	7
Interest expense	(14)	(13)	(41)	(39)
Other income (expense)	(2)	(6)	4	(5)
Income (loss) from continuing operations before income taxes and equity in earnings of affiliated companies	95	68	16	221
(Provision) benefit for income taxes	4	(16)	(194)	(33)
Equity in earnings of affiliated companies, net of tax		3	2	6
Net income (loss)	99	55	(176)	194
Net income (loss) attributable to noncontrolling interests, net of tax	11	8	31	18
Net income (loss) attributable to Cabot Corporation	$ 88	$ 47	$ (207)	$ 176
Weighted-average common shares outstanding:
Basic	61.8	62.4	61.8	62.3
Diluted	62.3	62.7	61.8	62.8
Earnings per common share:
Basic	$ 1.41	$ 0.73	$ (3.36)	$ 2.79
Diluted	1.40	0.73	(3.36)	2.78
Dividends per common share	$ 0.33	$ 0.315	$ 0.96	$ 0.915
Purification Solutions [Member]
Long-lived assets impairment (Note E)			$ 162
Goodwill impairment (Note E)			$ 92