Derivatives and Other Financial Instruments - Gross Amounts of Recognized Derivative Assets and Liabilities and Gross Amounts Offset in Accompanying Consolidated Balance Sheet (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross amounts recognized	$ 146	$ 117
Gross amounts offset	(108)	(72)
Net amount presented in Consolidated Balance Sheet	470	596
Gross amounts recognized	177	86
Gross amounts offset	(108)	(72)
Net amount presented in Consolidated Balance Sheet	69	14
Aluminum Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross amounts recognized	110	72
Gross amounts offset	(104)	(55)
Net amount presented in Consolidated Balance Sheet	6	17
Gross amounts recognized	171	69
Gross amounts offset	(104)	(55)
Net amount presented in Consolidated Balance Sheet	67	14
Interest Rate Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross amounts recognized	35	45
Gross amounts offset	(3)	(17)
Net amount presented in Consolidated Balance Sheet	32	28
Gross amounts recognized	3	17
Gross amounts offset	(3)	(17)
Foreign Exchange Contracts [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Gross amounts recognized	1
Gross amounts offset	(1)
Gross amounts recognized	3
Gross amounts offset	(1)
Net amount presented in Consolidated Balance Sheet	$ 2