Consolidated Statements of Operations (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				9 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Income Statement [Abstract]
Net sales and other operating revenues	$ 940	[1]	$ 901	[1]	$ 2,736	[1]	$ 2,560	[1]
Cost of sales	756		725		2,197		2,094
Gross profit	184		176		539		466
Selling and administrative expenses	76		72		245		222
Research and technical expenses	15		17		46		50
Income from operations	93		87		248		194
Interest and dividend income	1		2		3		4
Interest expense	(14)		(15)		(41)		(47)
Other income					27		3
Income from continuing operations before income taxes and equity in (loss) earnings of affiliated companies	80	[2]	74	[2]	237	[2]	154	[2]
Provision for income taxes	(20)		(16)		(51)		(52)
Equity in (loss) earnings of affiliated companies, net of tax	(2)		3		(2)		9
Income from continuing operations	58		61		184		111
(Loss) income from discontinued operations, net of tax	(1)		1		(2)		(2)
Net income	57		62		182		109
Net income attributable to noncontrolling interests, net of tax	5		3		14		3
Net income attributable to Cabot Corporation	$ 52		$ 59		$ 168		$ 106
Weighted-average common shares outstanding, in millions:
Basic	64.5		63.8		64.3		63.6
Diluted	65.2		64.5		65.0		64.3
Basic:
Income from continuing operations attributable to Cabot Corporation	$ 0.80		$ 0.88		$ 2.61		$ 1.66
(Loss) income from discontinued operations	$ (0.01)		$ 0.04		$ (0.03)		$ (0.01)
Net income attributable to Cabot Corporation	$ 0.79		$ 0.92		$ 2.58		$ 1.65
Diluted:
Income from continuing operations attributable to Cabot Corporation	$ 0.79		$ 0.87		$ 2.58		$ 1.64
(Loss) income from discontinued operations	$ (0.01)		$ 0.03		$ (0.03)		$ (0.01)
Net income attributable to Cabot Corporation	$ 0.78		$ 0.90		$ 2.55		$ 1.63
Dividends per common share	$ 0.22		$ 0.20		$ 0.62		$ 0.60

[1] Revenue from external customers that are categorized as Unallocated and Other reflects royalties, other operating revenues, external shipping and handling costs, the impact of unearned revenue, the removal of 100% of the sales of an equity method affiliate and discounting charges for certain Notes receivable. Details are provided in the table below:

[2] Income (loss) from continuing operations before taxes that are categorized as Unallocated and Other includes: