Consolidated Statements of Comprehensive Income (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Accumulated Other Comprehensive Income Loss Net Of Tax [Abstract]
Net income	$ 57	$ 62	$ 182	$ 109
Other comprehensive income (loss), net of tax
Foreign currency translation adjustment (net of tax provision (benefit) of $-, $2, $1, and $(12))	11	(16)	(18)	(38)
Unrealized holding gains arising during the period (net of tax provision of $1, $-, $1, and $-)	2	1	2	1
Pension and other postretirement benefit liability adjustments
Pension and other postretirement benefit liability adjustments arising during the period (net of tax provision of $-, $6, $-, and $6)		13		15
Amortization of net loss and prior service credit included in net periodic pension cost (net of tax provision of $-, $-, $-, and $2)			1	1
Other comprehensive income (loss)	13	(2)	(15)	(21)
Comprehensive income	70	60	167	88
Net income attributable to noncontrolling interests	5	3	14	3
Noncontrolling interests foreign currency translation adjustment, net of tax		2	(2)	1
Comprehensive income attributable to noncontrolling interests, net of tax	5	5	12	4
Comprehensive income attributable to Cabot Corporation	$ 65	$ 55	$ 155	$ 84