Other Noncurrent Liabilities and Deferred Credits - Schedule of Other Noncurrent Liabilities and Deferred Credits (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Other Liabilities And Deferred Credits [Line Items]
Fair value of derivative contracts (X)	$ 606	$ 624
Asset retirement obligations (C)	535	503
Environmental remediation (N)	458	289
Deferred income taxes (T)	460	395
Deferred credit related to derivative contract (X)	330
Accrued compensation and retirement costs	322	304
Deferred alumina sales revenue	108	116
Other	259	197
Other noncurrent liabilities and deferred credits, total	$ 3,078	$ 2,428