Derivatives - Schedule of Derivatives Foreign Currency (Detail) (Not Designated as Hedging Instrument [Member], Forward Foreign Currency Contracts [Member], USD $) In Millions, unless otherwise specified	Jun. 30, 2014		Sep. 30, 2013
Not Designated as Hedging Instrument [Member] | Forward Foreign Currency Contracts [Member]
Derivative [Line Items]
Notional amount of forward foreign currency contract no designation hedge derivatives	$ 13	[1]	$ 31	[1]

[1] Cabot's forward foreign exchange contracts are denominated primarily in the Brazilian real, British pound sterling, , Chinese renminbi, Czech koruna and Indian rupee.