XML 1184 R157.htm IDEA: XBRL DOCUMENT

Derivatives and Other Financial Instruments - Schedule of Outstanding Forward Contracts that were Entered into Hedge Forecasted Transactions (Detail) (USD $) In Millions, unless otherwise specified			12 Months Ended
	Dec. 31, 2012 Energy Contracts [Member] MWh Btu	Dec. 31, 2011 Energy Contracts [Member] MWh	Dec. 31, 2012 Foreign Exchange Contracts [Member]	Dec. 31, 2012 Aluminum Contracts [Member] Mg	Dec. 31, 2011 Aluminum Contracts [Member] Mg
Derivative Instruments, Gain (Loss) [Line Items]
Aluminum contracts (kmt)				1,120	1,294
Electricity (megawatt hours)	100,578,295	100,578,295
Natural gas (million British thermal units)	19,160,000
Foreign exchange contracts			$ 71