Schedule Of Fair Value Gains And Losses On Derivatives Contracts Recorded In Earnings (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings on Derivatives	$ (8)	$ 16	$ (12)	$ 28
Sales \| Aluminum Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings on Derivatives	(6)	(2)	(3)	1
Other Expenses (Income), Net \| Aluminum Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings on Derivatives	10	3	3	(11)
Other Expenses (Income), Net \| Embedded Credit Derivative
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings on Derivatives	(10)	(6)	(10)	3
Other Expenses (Income), Net \| Energy Contracts
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings on Derivatives		19		31
Other Expenses (Income), Net \| Foreign Exchange Contract
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Gain or (Loss) Recognized in Earnings on Derivatives	$ (2)	$ 2	$ (2)	$ 4