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
	Mar. 31, 2013	Mar. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings on Derivatives	$ (68)	$ 39
Amount of Gain or (Loss) Recognized in Earnings on Hedged Items	68	(51)
Aluminum contracts [Member] | Sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings on Derivatives	(71)	36
Amount of Gain or (Loss) Recognized in Earnings on Hedged Items	71	(48)
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
Amount of Gain or (Loss) Recognized in Earnings on Hedged Items	$ (3)	$ (3)