Derivatives and Other Financial Instruments - Schedule of Gain or Loss on Hedged Items and Derivative Contracts (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings on Derivatives	$ 23	$ 23	$ 27		$ (102)
Amount of Gain or (Loss) Recognized in Earnings on Hedged Items	(22)	(5)	(39)	124
Aluminum Contracts [Member] | Sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings on Derivatives	20	20	19		(110)
Amount of Gain or (Loss) Recognized in Earnings on Hedged Items	(19)	(2)	(31)	132
Interest Rate Contracts [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings on Derivatives	3	3	8		8
Amount of Gain or (Loss) Recognized in Earnings on Hedged Items	$ (3)	$ (3)	$ (8)	$ (8)