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	Jun. 30, 2013	Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	$ 470	$ 596
Level 1 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	6	27
Level 3 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	432	550
Level 2 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	35	45
Aluminum Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	6	17
Interest Rate Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	32	28
Derivatives Designated as Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	61	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	6	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	9	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	9	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
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	11
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	26	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
Derivatives Not Designated as Hedging Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	412	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	194	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	218	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]
Derivative Instruments, Gain (Loss) [Line Items]
Fair value asset derivatives	3	26
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	3	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