Derivatives and Other Financial Instruments - Schedule of Gains and Losses on Derivative Excluded from Assessment of Effectiveness Recognized in Current Earnings (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in OCI on Derivatives (Effective Portion)	$ (24)	$ (56)	$ (24)	$ 120
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)	(5)	(6)	(14)	(14)
Amount of Gain or (Loss) Recognized in Earnings on Derivatives (Ineffective Portion and Amount Excluded from Effectiveness Testing)	(5)		(1)	(2)
Aluminum Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in OCI on Derivatives (Effective Portion)	(2)	(61)	(21)	117
Aluminum Contracts [Member] | Other Expenses (Income), 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)			(1)	(2)
Aluminum Contracts [Member] | Sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)	(6)	(4)	(15)	(11)
Energy Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in OCI on Derivatives (Effective Portion)	(21)	1	(6)
Energy Contracts [Member] | Other Expenses (Income), 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)	(5)
Foreign Exchange Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in OCI on Derivatives (Effective Portion)	(1)	3	1	1
Foreign Exchange Contracts [Member] | Sales [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)		(2)	1	(2)
Interest Rate Contracts [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Reclassified from Accumulated OCI into Earnings (Effective Portion)	1			(1)
Interest Rate Contract 2 [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in OCI on Derivatives (Effective Portion)		$ 1	$ 2	$ 2