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Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended |
--- | --- | ---
Mar. 31, 2015 | Dec. 31, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Assets, Fair value | $ 209 us-gaap_DerivativeFairValueOfDerivativeAsset | $ 268 us-gaap_DerivativeFairValueOfDerivativeAsset
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Assets, Fair value | 140 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember |
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 1,798 us-gaap_UnderlyingDerivativeMass / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity year of future aluminum price | 2015 |
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 1,869 us-gaap_UnderlyingDerivativeMass / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity year of future aluminum price | 2016 |
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Estimated Foreign Currency Exchange Rate [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Foreign currency exchange rate | 0.77 us-gaap_UnderlyingDerivativeAsset / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_EstimatedForeignCurrencyExchangeRateMember |
Foreign currency exchange rate expected year | 2015 |
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Estimated Foreign Currency Exchange Rate [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Foreign currency exchange rate | 0.78 us-gaap_UnderlyingDerivativeAsset / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_EstimatedForeignCurrencyExchangeRateMember |
Foreign currency exchange rate expected year | 2016 |
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Consumer Price Index [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected consumer price index | 231 aa_ExpectedConsumerPriceIndex / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_ConsumerPriceIndexMember |
Expected consumer price index, Year | 2015 |
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Consumer Price Index [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Consumer price index base year | 1982 |
Consumer price index base | 100 aa_BaseYearConsumerPriceIndex / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_ConsumerPriceIndexMember |
Expected consumer price index | 239 aa_ExpectedConsumerPriceIndex / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfFutureAluminumPricesForeignCurrencyExchangeRatesAndUSConsumerPriceIndexMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_ConsumerPriceIndexMember |
Expected consumer price index, Year | 2016 |
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum and Oil Prices [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 1,798 us-gaap_UnderlyingDerivativeMass / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfFutureAluminumAndOilPricesMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity year of future aluminum price | 2015 |
Expected future oil prices | 56 us-gaap_UnderlyingDerivativeVolume / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfFutureAluminumAndOilPricesMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity year of future oil price | 2015 |
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum and Oil Prices [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 1,983 us-gaap_UnderlyingDerivativeMass / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfFutureAluminumAndOilPricesMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity year of future aluminum price | 2018 |
Expected future oil prices | 71 us-gaap_UnderlyingDerivativeVolume / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfFutureAluminumAndOilPricesMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity year of future oil price | 2018 |
Assets [Member] | Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 2,320 us-gaap_UnderlyingDerivativeMass / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_PriceOfAluminumBeyondForwardCurveMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity year of future aluminum price | 2025 |
Assets [Member] | Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 2,425 us-gaap_UnderlyingDerivativeMass / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_PriceOfAluminumBeyondForwardCurveMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity year of future aluminum price | 2027 |
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of LME Price to Overall Energy Price [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 1,830 us-gaap_UnderlyingDerivativeMass / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfLondonMetalExchangePriceToOverallEnergyPriceMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity year of future aluminum price | 2015 |
Assets [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of LME Price to Overall Energy Price [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 2,003 us-gaap_UnderlyingDerivativeMass / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfLondonMetalExchangePriceToOverallEnergyPriceMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity year of future aluminum price | 2019 |
Assets [Member] | Energy Contracts [Member] | Price of Electricity beyond Forward Curve [Member] | Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Assets, Fair value | 8 us-gaap_DerivativeFairValueOfDerivativeAsset / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EnergyContractsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_PriceOfElectricityBeyondForwardCurveMember |
Assets [Member] | Energy Contracts [Member] | Price of Electricity beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Price of electricity beyond forward curve | 43 us-gaap_UnderlyingDerivativeEnergyMeasure / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EnergyContractsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_PriceOfElectricityBeyondForwardCurveMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity date of electricity beyond forward curve | 2018 |
Assets [Member] | Energy Contracts [Member] | Price of Electricity beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Price of electricity beyond forward curve | 130 us-gaap_UnderlyingDerivativeEnergyMeasure / us-gaap_BalanceSheetLocationAxis = us-gaap_AssetsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EnergyContractsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_PriceOfElectricityBeyondForwardCurveMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity date of electricity beyond forward curve | 2036 |
Liability [Member] | Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Liabilities, Fair value | 344 us-gaap_DerivativeAssetFairValueGrossLiability / us-gaap_BalanceSheetLocationAxis = us-gaap_LiabilityMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_PriceOfAluminumBeyondForwardCurveMember |
Liability [Member] | Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 2,320 us-gaap_UnderlyingDerivativeMass / us-gaap_BalanceSheetLocationAxis = us-gaap_LiabilityMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_PriceOfAluminumBeyondForwardCurveMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity year of future aluminum price | 2025 |
Liability [Member] | Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Midwest Premium | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Midwest Premium | 0.1725 us-gaap_UnderlyingDerivative / us-gaap_BalanceSheetLocationAxis = us-gaap_LiabilityMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_PriceOfAluminumBeyondForwardCurveMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_MarketRiskPremiumMember |
Foreign currency exchange rate expected year | 2020 |
Liability [Member] | Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Midwest Premium | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Midwest Premium | 0.1725 us-gaap_UnderlyingDerivative / us-gaap_BalanceSheetLocationAxis = us-gaap_LiabilityMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_PriceOfAluminumBeyondForwardCurveMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_MarketRiskPremiumMember |
Liability [Member] | Embedded Aluminum Derivative [Member] | Interrelationship of LME Price to Overall Energy Price [Member] | Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Liabilities, Fair value | 16 us-gaap_DerivativeAssetFairValueGrossLiability / us-gaap_BalanceSheetLocationAxis = us-gaap_LiabilityMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_InterrelationshipOfLondonMetalExchangePriceToOverallEnergyPriceMember |
Liability [Member] | Embedded Aluminum Derivative [Member] | Two Contracts [Member] | Price of Aluminum beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 2,533 us-gaap_UnderlyingDerivativeMass / us-gaap_BalanceSheetLocationAxis = us-gaap_LiabilityMember / us-gaap_CreditDerivativesByContractTypeAxis = aa_TwoContractsMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_PriceOfAluminumBeyondForwardCurveMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity year of future aluminum price | 2029 |
Liability [Member] | Embedded Aluminum Derivative [Member] | Two Contracts [Member] | Price of Aluminum beyond Forward Curve [Member] | Midwest Premium | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Foreign currency exchange rate expected year | 2029 |
Liability [Member] | Embedded Aluminum Derivative [Member] | One Contract [Member] | Price of Aluminum beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 2,870 us-gaap_UnderlyingDerivativeMass / us-gaap_BalanceSheetLocationAxis = us-gaap_LiabilityMember / us-gaap_CreditDerivativesByContractTypeAxis = aa_OneContractMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_PriceOfAluminumBeyondForwardCurveMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_AveragePriceMember |
Maturity year of future aluminum price | 2036 |
Liability [Member] | Embedded Aluminum Derivative [Member] | One Contract [Member] | Price of Aluminum beyond Forward Curve [Member] | Midwest Premium | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Foreign currency exchange rate expected year | 2036 |
Liability [Member] | Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Liabilities, Fair value | 16 us-gaap_DerivativeAssetFairValueGrossLiability / us-gaap_BalanceSheetLocationAxis = us-gaap_LiabilityMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedCreditDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_CreditSpreadBetweenAlcoaAndCounterpartyMember |
Liability [Member] | Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Credit Spread [Member] | Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Percentage of credit spread | 1.44%aa_AveragePercentageOfCreditSpread / us-gaap_BalanceSheetLocationAxis = us-gaap_LiabilityMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedCreditDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_CreditSpreadBetweenAlcoaAndCounterpartyMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_CreditSpreadMember |
Liability [Member] | Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Credit Spread [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Percentage of credit spread | 1.17%aa_AveragePercentageOfCreditSpread / us-gaap_BalanceSheetLocationAxis = us-gaap_LiabilityMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedCreditDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_CreditSpreadBetweenAlcoaAndCounterpartyMember / us-gaap_RangeAxis = us-gaap_MinimumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_CreditSpreadMember |
Liability [Member] | Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Credit Spread [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Percentage of credit spread | 1.70%aa_AveragePercentageOfCreditSpread / us-gaap_BalanceSheetLocationAxis = us-gaap_LiabilityMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedCreditDerivativeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_CreditSpreadBetweenAlcoaAndCounterpartyMember / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_UnusualRiskOrUncertaintyByNatureAxis = aa_CreditSpreadMember |
Liability [Member] | Embedded Aluminum Derivatives [Member] | Price of Aluminum beyond Forward Curve [Member] | Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Liabilities, Fair value | $ 4 us-gaap_DerivativeAssetFairValueGrossLiability / us-gaap_BalanceSheetLocationAxis = us-gaap_LiabilityMember / us-gaap_DerivativeInstrumentRiskAxis = aa_EmbeddedAluminumDerivativesMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementBasisAxis = aa_PriceOfAluminumBeyondForwardCurveMember |

X
- Definition Average percentage of credit spread. + References No definition available. + Details
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X
- Definition Base year consumer price index. + References No definition available. + Details
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Namespace Prefix: | aa_
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- Definition Consumer price index base year. + References No definition available. + Details
Name: | aa_ConsumerPriceIndexBaseYear
Namespace Prefix: | aa_
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Balance Type: | na
Period Type: | duration

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- Definition Expected consumer price index. + References No definition available. + Details
Name: | aa_ExpectedConsumerPriceIndex
Namespace Prefix: | aa_
Data Type: | xbrli:integerItemType
Balance Type: | na
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