Derivatives and Other Financial Instruments - Schedule of Outstanding Forward Contracts that were Entered into Hedge Forecasted Transactions (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013 t	Dec. 31, 2012 t
Aluminum Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Aluminum contracts (000 metric tons)	841,000	1,120,000
Energy Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Electricity (megawatt hours)	59,409,328	100,578,295
Natural gas (million British thermal units)	19,980,000	19,160,000
Foreign Exchange Contracts [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Foreign exchange contracts	$ 335	$ 71