Derivatives and Other Financial Instruments - Schedule of Fair Values and Corresponding Level of Fair Value Hierarchy of Outstanding Derivative Contracts Recorded as Assets (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	$ 563	$ 596
Level 1 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	5	27
Level 3 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	530	550
Level 2 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	42	45
Aluminum contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	5	17
Interest rate contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	28	28
Other noncurrent assets [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	14	26
Derivatives designated as hedging instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	67	81
Derivatives designated as hedging instruments [Member] | Prepaid expenses and other current assets [Member] | Aluminum contracts [Member] | Level 1 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	4	23
Derivatives designated as hedging instruments [Member] | Prepaid expenses and other current assets [Member] | Aluminum contracts [Member] | Level 3 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	8	7
Derivatives designated as hedging instruments [Member] | Prepaid expenses and other current assets [Member] | Interest rate contracts [Member] | Level 2 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	5	8
Derivatives designated as hedging instruments [Member] | Other noncurrent assets [Member] | Aluminum contracts [Member] | Level 1 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	1	3
Derivatives designated as hedging instruments [Member] | Other noncurrent assets [Member] | Aluminum contracts [Member] | Level 3 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	4
Derivatives designated as hedging instruments [Member] | Other noncurrent assets [Member] | Interest rate contracts [Member] | Level 2 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	37	37
Derivatives designated as hedging instruments [Member] | Other noncurrent assets [Member] | Energy contracts [Member] | Level 3 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	8	3
Derivatives not designated as hedging instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	510	541
Derivatives not designated as hedging instruments [Member] | Prepaid expenses and other current assets [Member] | Aluminum contracts [Member] | Level 3 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	216	211
Derivatives not designated as hedging instruments [Member] | Other noncurrent assets [Member] | Aluminum contracts [Member] | Level 3 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	294	329
Derivatives not designated as hedging instruments [Member] | Other noncurrent assets [Member] | Foreign exchange contracts [Member] | Level 1 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives		1
Margin held [Member] | Prepaid expenses and other current assets [Member] | Aluminum contracts [Member] | Level 1 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives		9
Margin held [Member] | Prepaid expenses and other current assets [Member] | Interest rate contracts [Member] | Level 2 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	5	8
Margin held [Member] | Other noncurrent assets [Member] | Interest rate contracts [Member] | Level 2 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	$ 9	$ 9