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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 | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2013 | Dec. 31, 2012
Energy contracts [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Electricity (megawatt hours) | 59,409,328 | 100,578,295
Natural gas (million British thermal units) | 19,250,000 | 19,160,000
Foreign exchange contracts [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Foreign exchange contracts | $ 86 | $ 71
Aluminum contracts [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Aluminum contracts (kmt) | 1,085 | 1,120

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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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Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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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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Namespace Prefix: | aa_
Data Type: | xbrli:integerItemType
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Period Type: | instant

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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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Namespace Prefix: | aa_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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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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Namespace Prefix: | aa_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

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- Details
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Namespace Prefix: | us-gaap_
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Period Type: | duration