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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 |  |

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- Definition Outstanding Forward Contracts Entered Into As Hedge Forecasted Transactions, Foreign Exchange Contracts + References No definition available. + Details
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- Definition Outstanding Forward Contracts Entered Into As Hedge Forecasted Transactions Measured In British Thermal Units + References No definition available. + Details
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- Definition Outstanding forward contracts entered into as hedge forecasted transactions measured in mega watt hours. + References No definition available. + Details
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- Definition Outstanding forward contracts entered into as hedging forecasted transactions measured in kilo metric ton. + References No definition available. + Details
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- Details
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