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Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) (USD $)
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative Assets, Fair value $ 268,000,000us-gaap_DerivativeFairValueOfDerivativeAsset $ 355,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Embedded Aluminum Derivative [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative Assets, Fair value 168,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
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= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember		  
Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Embedded Aluminum Derivative [Member] | Minimum [Member] | Discounted Cash Flow [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Expected future aluminum prices 1,841aa_ExpectedFutureAluminumPrices
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/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Maturity year of future aluminum price 2015  
Foreign currency exchange rate 1us-gaap_ForeignCurrencyExchangeRateRemeasurement1
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Foreign currency exchange rate 0.82us-gaap_ForeignCurrencyExchangeRateTranslation1
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Embedded Aluminum Derivative [Member] | Minimum [Member] | Discounted Cash Flow [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Foreign currency exchange rate expected year 2015  
Expected consumer price index 233aa_ExpectedConsumerPriceIndex
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= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Expected consumer price index, Year 2015  
Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Embedded Aluminum Derivative [Member] | Maximum [Member] | Discounted Cash Flow [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Expected future aluminum prices 1,923aa_ExpectedFutureAluminumPrices
/ us-gaap_DerivativeInstrumentRiskAxis
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/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Maturity year of future aluminum price 2016  
Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Embedded Aluminum Derivative [Member] | Maximum [Member] | Discounted Cash Flow [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Foreign currency exchange rate 0.83us-gaap_ForeignCurrencyExchangeRateTranslation1
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/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
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/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Foreign currency exchange rate expected year 2016  
Consumer price index base year 1982  
Consumer price index base 100aa_BaseYearConsumerPriceIndex
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/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Expected consumer price index 242aa_ExpectedConsumerPriceIndex
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Expected consumer price index, Year 2016  
Price of Aluminum beyond Forward Curve [Member] | Embedded Aluminum Derivative [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative Assets, Fair value 77,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_FairValueByAssetClassAxis
= aa_PriceOfAluminumBeyondForwardCurveMember		  
Price of Aluminum beyond Forward Curve [Member] | Embedded Aluminum Derivative [Member] | Liability [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative Assets, Fair value 357,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
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= us-gaap_LiabilityMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_FairValueByAssetClassAxis
= aa_PriceOfAluminumBeyondForwardCurveMember		  
Price of Aluminum beyond Forward Curve [Member] | Embedded Aluminum Derivative [Member] | Minimum [Member] | Discounted Cash Flow [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Expected future aluminum prices 2,332aa_ExpectedFutureAluminumPrices
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/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_PriceOfAluminumBeyondForwardCurveMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Maturity year of future aluminum price 2025  
Foreign currency exchange rate 0.2315us-gaap_ForeignCurrencyExchangeRateTranslation1
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_PriceOfAluminumBeyondForwardCurveMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Foreign currency exchange rate expected year 2020  
Price of Aluminum beyond Forward Curve [Member] | Embedded Aluminum Derivative [Member] | Minimum [Member] | Discounted Cash Flow [Member] | Liability [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Price of aluminum beyond forward curve 2,332aa_ExpectedPriceOfAluminumThroughForwardCurve
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_LiabilityMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_PriceOfAluminumBeyondForwardCurveMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Maturity year of future aluminum price 2025  
Price of Aluminum beyond Forward Curve [Member] | Embedded Aluminum Derivative [Member] | Maximum [Member] | Discounted Cash Flow [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Expected future aluminum prices 2,558aa_ExpectedFutureAluminumPrices
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_PriceOfAluminumBeyondForwardCurveMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Maturity year of future aluminum price 2029  
Foreign currency exchange rate 0.2315us-gaap_ForeignCurrencyExchangeRateTranslation1
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= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_PriceOfAluminumBeyondForwardCurveMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Price of Aluminum beyond Forward Curve [Member] | Embedded Aluminum Derivative [Member] | Maximum [Member] | Discounted Cash Flow [Member] | Liability [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Price of aluminum beyond forward curve 2,449aa_ExpectedPriceOfAluminumThroughForwardCurve
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_LiabilityMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_PriceOfAluminumBeyondForwardCurveMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Maturity year of future aluminum price 2027  
Price of Aluminum beyond Forward Curve [Member] | Embedded Aluminum Derivative [Member] | Maximum [Member] | Discounted Cash Flow [Member] | Two Contracts [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Foreign currency exchange rate expected year 2029  
Price of Aluminum beyond Forward Curve [Member] | Embedded Aluminum Derivative [Member] | Maximum [Member] | Discounted Cash Flow [Member] | One Contract [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Foreign currency exchange rate expected year 2036  
Interrelationship of LME Price to Overall Energy Price [Member] | Embedded Aluminum Derivative [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative Assets, Fair value 1,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
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= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfLondonMetalExchangePriceToOverallEnergyPriceMember		  
Interrelationship of LME Price to Overall Energy Price [Member] | Embedded Aluminum Derivative [Member] | Minimum [Member] | Discounted Cash Flow [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Expected future aluminum prices 1,910aa_ExpectedFutureAluminumPrices
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfLondonMetalExchangePriceToOverallEnergyPriceMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Maturity year of future aluminum price 2015  
Interrelationship of LME Price to Overall Energy Price [Member] | Embedded Aluminum Derivative [Member] | Maximum [Member] | Discounted Cash Flow [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Expected future aluminum prices 2,040aa_ExpectedFutureAluminumPrices
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfLondonMetalExchangePriceToOverallEnergyPriceMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Maturity year of future aluminum price 2019  
Interrelationship of Future Aluminum and Oil Prices [Member] | Embedded Aluminum Derivative [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative Assets, Fair value 1,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfFutureAluminumAndOilPricesMember		  
Interrelationship of Future Aluminum and Oil Prices [Member] | Embedded Aluminum Derivative [Member] | Minimum [Member] | Discounted Cash Flow [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Expected future aluminum prices 1,841aa_ExpectedFutureAluminumPrices
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfFutureAluminumAndOilPricesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Maturity year of future aluminum price 2015  
Expected future oil prices 58aa_ExpectedFutureOilPrices
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
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= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfFutureAluminumAndOilPricesMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Maturity year of future oil price 2015  
Interrelationship of Future Aluminum and Oil Prices [Member] | Embedded Aluminum Derivative [Member] | Maximum [Member] | Discounted Cash Flow [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Expected future aluminum prices 2,012aa_ExpectedFutureAluminumPrices
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfFutureAluminumAndOilPricesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Maturity year of future aluminum price 2018  
Expected future oil prices 76aa_ExpectedFutureOilPrices
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_AssetsMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedAluminumDerivativeMember
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= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_InterrelationshipOfFutureAluminumAndOilPricesMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Maturity year of future oil price 2018  
Price of Electricity beyond Forward Curve [Member] | Energy Contracts [Member] | Liability [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative Assets, Fair value 2,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
= us-gaap_LiabilityMember
/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EnergyContractsMember
/ us-gaap_FairValueByAssetClassAxis
= aa_PriceOfElectricityBeyondForwardCurveMember		  
Price of Electricity beyond Forward Curve [Member] | Energy Contracts [Member] | Minimum [Member] | Discounted Cash Flow [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Price of electricity beyond forward curve 43aa_PriceOfElectricityThroughForwardCurve
/ us-gaap_BalanceSheetLocationAxis
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/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EnergyContractsMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_PriceOfElectricityBeyondForwardCurveMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Maturity date of electricity beyond forward curve 2018  
Price of Electricity beyond Forward Curve [Member] | Energy Contracts [Member] | Maximum [Member] | Discounted Cash Flow [Member] | Assets [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Price of electricity beyond forward curve 130aa_PriceOfElectricityThroughForwardCurve
/ us-gaap_BalanceSheetLocationAxis
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/ us-gaap_DerivativeInstrumentRiskAxis
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/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_PriceOfElectricityBeyondForwardCurveMember
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		  
Maturity date of electricity beyond forward curve 2036  
Credit Spread between Alcoa and Counterparty [Member] | Embedded Credit Derivative [Member] | Liability [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Derivative Assets, Fair value $ 18,000,000us-gaap_DerivativeFairValueOfDerivativeAsset
/ us-gaap_BalanceSheetLocationAxis
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/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedCreditDerivativeMember
/ us-gaap_FairValueByAssetClassAxis
= aa_CreditSpreadBetweenAlcoaAndCounterpartyMember		  
Credit Spread between Alcoa and Counterparty [Member] | Embedded Credit Derivative [Member] | Discounted Cash Flow [Member] | Liability [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Percentage of credit spread 1.60%aa_AveragePercentageOfCreditSpread
/ us-gaap_BalanceSheetLocationAxis
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/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedCreditDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_CreditSpreadBetweenAlcoaAndCounterpartyMember		  
Credit Spread between Alcoa and Counterparty [Member] | Embedded Credit Derivative [Member] | Minimum [Member] | Discounted Cash Flow [Member] | Liability [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Percentage of credit spread 1.35%aa_AveragePercentageOfCreditSpread
/ us-gaap_BalanceSheetLocationAxis
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/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedCreditDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
= aa_CreditSpreadBetweenAlcoaAndCounterpartyMember
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		  
Credit Spread between Alcoa and Counterparty [Member] | Embedded Credit Derivative [Member] | Maximum [Member] | Discounted Cash Flow [Member] | Liability [Member]    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Percentage of credit spread 1.85%aa_AveragePercentageOfCreditSpread
/ us-gaap_BalanceSheetLocationAxis
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/ us-gaap_DerivativeInstrumentRiskAxis
= aa_EmbeddedCreditDerivativeMember
/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis
= aa_DiscountedCashFlowMember
/ us-gaap_FairValueByAssetClassAxis
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/ us-gaap_RangeAxis
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