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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 | Sep. 30, 2014 t | Dec. 31, 2013 t
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Aluminum Contracts [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Aluminum contracts (000 metric tons) | 707,000 | 841,000
Energy Contracts [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Electricity (megawatt hours) | 59,409,328 | 59,409,328
Natural gas (million British thermal units) | 20,570,000 | 19,980,000
Foreign Exchange Contracts [Member] |  |
Derivative Instruments, Gain (Loss) [Line Items] |  |
Foreign exchange contracts | $ 632 | $ 335

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

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- Details
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