Derivatives and Other Financial Instruments - Schedule of Net Fair Values of Outstanding Derivative Contracts and Effect of Hypothetical Change (Increase or Decrease of 10%) in Market Prices or Rates (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Aluminum Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset/(liability)	$ (85)
Index change of + / - 10%	111
Embedded Credit Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset/(liability)	(30)
Index change of + / - 10%	3
Energy Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset/(liability)	3
Index change of + / - 10%	249
Foreign Exchange Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset/(liability)	1
Index change of + / - 10%	8
Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset/(liability)	28
Index change of + / - 10%	$ 1