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	Dec. 31, 2012	Dec. 31, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	$ 596	$ 94
Level 1 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	27	57
Level 3 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	550	12
Level 2 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	45	47
Other Noncurrent Assets [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	26	22
Derivatives Designated as Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	81	109
Derivatives Designated as Hedging Instruments [Member] | Prepaid Expense and Other Current Assets [Member] | Aluminum Contracts [Member] | Level 1 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	23	51
Derivatives Designated as Hedging Instruments [Member] | Prepaid Expense and Other Current Assets [Member] | Aluminum Contracts [Member] | Level 3 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	7	5
Derivatives Designated as Hedging Instruments [Member] | Prepaid Expense and Other Current Assets [Member] | Interest Rate Contracts [Member] | Level 2 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	8	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	3	6
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	3	2
Derivatives Not Designated as Hedging Instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	541	7
Derivatives Not Designated as Hedging Instrument [Member] | Prepaid Expense and Other Current Assets [Member] | Aluminum Contracts [Member] | Level 3 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	211
Derivatives Not Designated as Hedging Instrument [Member] | Prepaid Expense and Other Current Assets [Member] | Aluminum Contracts [Member] | Level 2 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives		1
Derivatives Not Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member] | Aluminum Contracts [Member] | Level 3 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	329	5
Derivatives Not Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member] | Foreign Exchange Contracts [Member] | Level 1 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	1	1
Margin Held [Member] | Prepaid Expense and Other Current Assets [Member] | Aluminum Contracts [Member] | Level 1 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	9	7
Margin Held [Member] | Prepaid Expense and Other Current Assets [Member] | Interest Rate Contracts [Member] | Level 2 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	8	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	$ 7