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Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Parenthetical) (Detail) (Aluminum Contracts [Member], USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2012
Aluminum Contracts [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Decrease in Fair value of assets and liabilities | $ 8

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The increase (decrease) during the period in the net carrying value of derivative instruments reported as assets and liabilities that are due to be disposed of within one year (or the normal operating cycle, if longer). + References No definition available. + Details
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Balance Type: | credit
Period Type: | duration