Derivatives and Other Financial Instruments - Schedule of Gains and Losses on Derivative Representing Either Hedge Ineffectiveness or Hedge Components Excluded from Assessment of Effectiveness are Recognized in Current Earnings (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing)	$ (3)	[1]	$ 4	[1]	$ 6	[1]	$ 4	[1]
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)	18	[2]	(32)	[2]	19	[2]	(114)	[2]
Amount of Gain or (Loss) Recognized in OCI on Derivatives (Effective Portion)	(135)		149		(77)		65
Amount of loss expected to be recognized into earnings over the next 12 months					14
Amount of gain or (loss) recognized in earnings related to ineffective portion of hedging relationships	(5)		(1)		5		(1)
Earnings recognized in relation to amount excluded from the assessment of hedge effectiveness	2		5		1		5
Aluminum Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in OCI on Derivatives (Effective Portion)	(138)		145		(72)		53
Aluminum Contracts [Member] | Sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)	18	[2]	(30)	[2]	20	[2]	(106)	[2]
Aluminum Contracts [Member] | Other (Income) Expenses, Net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing)	(3)	[1]	4	[1]	6	[1]	4	[1]
Energy Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in OCI on Derivatives (Effective Portion)	2		6		(3)		14
Energy Contracts [Member] | Cost of Goods Sold [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)			(2)	[2]			(8)	[2]
Foreign Exchange Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in OCI on Derivatives (Effective Portion)			2				4
Foreign Exchange Contract [Member] | Sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)			2	[2]			4	[2]
Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in OCI on Derivatives (Effective Portion)			(2)				(2)
Interest Rate Contract [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)			(2)	[2]	(1)	[2]	(2)	[2]
Interest Rate Contract [Member] | Other (Income) Expenses, Net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)							(2)	[2]
Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ 1		$ (2)		$ (2)		$ (4)

[1] For the third quarter and nine months ended September 30, 2012, the amount of gain or (loss) recognized in earnings represents $(5) and $5, respectively, related to the ineffective portion of the hedging relationships. There was also $2 and $1 recognized in earnings related to the amount excluded from the assessment of hedge effectiveness for the third quarter and nine months ended September 30, 2012, respectively. For both the third quarter and nine months ended September 30, 2011, the amount of gain or (loss) recognized in earnings represents $(1) related to the ineffective portion of the hedging relationships. There was also $5 recognized in earnings related to the amount excluded from the assessment of hedge effectiveness for both the third quarter and nine months ended September 30, 2011.

[2] Assuming market rates remain constant with the rates at September 30, 2012, a loss of $14 is expected to be recognized in earnings over the next 12 months.