<DefinitionAndReference>
  <Element Id="aa_OutstandingForwardContractsEnteredIntoAsHedgeForecastedTransactionsForeignExchangeContracts">
    <definition>Outstanding Forward Contracts Entered Into As Hedge Forecasted Transactions, Foreign Exchange Contracts</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_Assets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_OtherRestructuringActivitiesAfterTaxAndNoncontrollingInterests">
    <definition>Other restructuring activities, after tax and noncontrolling interests</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PreferredStockDividends">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_RecommendedCappingRemedyMin">
    <definition>Recommended Capping Remedy Min</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DebtInstrumentPeriodicPaymentPrincipal">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeLossFromEquityMethodInvestmentsNetOfDividendsOrDistributions">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EffectiveIncomeTaxRateReconciliationTaxSettlementsDomestic">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_GainLossOnFairValueHedgeIneffectivenessNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherReceivables">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_TreasuryStockValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_GainLossOnPriceRiskDerivativesNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccrualForEnvironmentalLossContingenciesPayments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_SegmentReportingInformationProfitLossTotal">
    <definition>Segment Reporting Information Profit Loss Total</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RestructuringCharges">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ShareBasedCompensationOptionAndIncentivePlansPolicyPolicyTextBlock">
    <definition>Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_AmountOfSoldReceivablesRemainUncollected">
    <definition>Amount Of Sold Receivables Remain Uncollected</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_RestructuringAndOtherChargesAfterTaxAndNoncontrollingInterests">
    <definition>Amount charged against earnings in the period after-tax and noncontrolling interests for incurred and estimated costs associated with exit from or disposal of business activities or restructurings pursuant to a program that is planned and controlled by management, and materially changes either the scope of a business undertaken by an entity, or the manner in which that business is conducted.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromRepaymentsOfShortTermDebt">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_NumberOfEmployees">
    <definition>Number of employees</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_InvestmentPercentage">
    <definition>Investment percentage</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_EstimatedDecreaseInNumberOfEmployeesDueToRestructuring">
    <definition>Estimated Decrease in Number of Employees Due to Restructuring</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LiabilitiesCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CashAndCashEquivalentsAtCarryingValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_CapitalInvestmentCommitmentPaidToDate">
    <definition>The amount of cash contributed by an entity through the most recent balance sheet date to a joint venture accounted for under the equity method related to asset construction costs.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ReconciliationOfActivityForDerivativeContractsOnNetBasisTextBlock">
    <definition>Reconciliation of activity for derivative contracts on a net basis [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeDerivativesQualifyingAsHedgesNetOfTaxPeriodIncreaseDecrease">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ScheduleOfComponentsOfNetPeriodicBenefitCostTextBlock">
    <definition>Schedule Of Components of Net Periodic Benefit Cost [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncrementalCommonSharesAttributableToNonvestedSharesWithForfeitableDividends">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromContributionsFromAffiliates">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfSegmentReportingInformationBySegmentTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_WeightedAverageExercisePriceOfUnderwaterOptions">
    <definition>The weighted average exercise price of stock options whose individual exercise prices were greater than the average market price of an entity's common stock during the period.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_FairValuesOfOutstandingDerivativeContractsRecordedAsLiabilitiesTextBlock">
    <definition>The fair values of outstanding derivative contracts recorded as liabilities [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InventoryFinishedGoodsNetOfReserves">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InventoryWriteDown">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DisposalGroupIncludingDiscontinuedOperationAccountsNotesAndLoansReceivableNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_TranslationAdjustmentFunctionalToReportingCurrencyIncreaseDecreaseGrossOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_Outstandingforwardcontractsenteredintoashedgeforecastedtransactionsmeasuredinmegawatthours">
    <definition>OutstandingForwardContractsEnteredIntoAsHedgeForecastedTransactionsMeasuredInMegawattHours</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_SegmentReportingInformationRestructuringAndOtherCharges">
    <definition>Segment Reporting Information Restructuring And Other Charges</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccrualForEnvironmentalLossContingencies">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DepreciationDepletionAndAmortization">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ConsiderationToBePaidForPurchasePerBaseOfNote">
    <definition>Consideration To Be Paid For Purchase Per Base of Note</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_SegmentReportingInformationRevenueTotal">
    <definition>Segment Reporting Information Revenue Total</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeInstrumentsGainLossRecognizedInIncomeNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_IncomeLossFromContinuingOperationsBeforeIncomeTaxes">
    <definition>Sum of operating profit and nonoperating income (expense) before income taxes, extraordinary items, cumulative effects of changes in accounting principles, and noncontrolling interest.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_RetiredFormerEmployeesInvolvedInClassAction">
    <definition>Retired former employees involved in class action</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInOtherOperatingLiabilities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EffectOfExchangeRateOnCashAndCashEquivalents">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeLossFromContinuingOperations">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock">
    <definition>New Accounting Pronouncements and Changes in Accounting Principles [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredTaxAssetsNetNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StockholdersEquityOther">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsForProceedsFromOtherInvestingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_IncomeLossFromContinuingOperationsAvailableToCommonShareholders">
    <definition>Income or loss from continuing operations after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period) and dividends and undistributed earnings allocated to participating securities.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ComponentOfOtherIncomeExpenseNonoperatingTableTextBlock">
    <definition>Provides a description and amount of each detailed component of other nonoperating income and expenses.  The description provided for other nonoperating income may include: (a) dividends, (b) interest on securities, (c) profits on securities (net of losses), and (d) miscellaneous other income items.  The description provided for other nonoperating expenses may include: (a) losses on securities (net of profits) and (b) miscellaneous income deductions.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InventoryRawMaterialsNetOfReserves">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_UnrealizedGainLossOnDerivatives">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StockIssuedDuringPeriodValueShareBasedCompensation">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InventoryWorkInProcessNetOfReserves">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockDividendsPerShareDeclared">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_GoodwillAllocationAdjustment">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PensionAndOtherPostretirementBenefitsDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ScheduleOfInventoryComponentsDisclosuresTableTextBlock">
    <definition>Disclosure of the carrying value of each significant component of inventory for an entity, who does not report such information on the face of their balance sheet.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityCentralIndexKey">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperation">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromStockOptionsExercised">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccountsReceivableNetCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_SegmentReportingInformationDepreciationDepletionAndAmortizationExpenseTotal">
    <definition>Segment Reporting Information Depreciation Depletion And Amortization Expense Total</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CostOfGoodsSoldDepreciationDepletionAndAmortization">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_SegmentReportingInformationCorporateExpenses">
    <definition>Segment Reporting Information Corporate Expenses</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="invest_InvestmentForeignCurrencyContractForeignCurrencyAmount">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanInterestCost">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DeferredIncomeTaxExpenseBenefit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_SegmentReportingInformationOtherIncomeExpenseNet">
    <definition>Segment Reporting Information Other Income Expense Net</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_TaxesPayableCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CostOfGoodsSold">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SellingGeneralAndAdministrativeExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EarningsPerShareDiluted">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DisposalGroupIncludingDiscontinuedOperationAccountsPayable">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_FinancialInstrumentsOwnedAtCarryingValue">
    <definition>Financial Instruments Owned At Carrying Value</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccruedEnvironmentalLossContingenciesCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_TotalInvestmentInMachadinhoProject">
    <definition>Total Investment in Machadinho Project</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShortTermBankLoansAndNotesPayable">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccountsPayableCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccrualForEnvironmentalLossContingenciesPeriodIncreaseDecrease">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeReclassificationAdjustmentForSaleOfSecuritiesIncludedInNetIncomeNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommitmentsAndContingencies2009">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetIncomeLossAttributableToNoncontrollingInterest">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityFilerCategory">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_EstimatedProjectCostOfConstructionAndMaintenance">
    <definition>Estimated Project Cost Of Construction And Maintenance</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherLiabilitiesNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInAccountsPayableTrade">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_AlcoaSDerivativeContractAssetsAndLiabilitiesThatAreMeasuredAndRecognizedAtFairValueOnRecurringBasisTextBlock">
    <definition>Alcoa's derivative contract assets and liabilities that are measured and recognized at fair value on a recurring basis [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecrease">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ContributionsFromNoncontrollingInterests">
    <definition>Contributions From Noncontrolling Interests</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LossContingencyRangeOfPossibleLossMinimum">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_IncreaseDecreaseInNetAssetsHeldForSale">
    <definition>The net change during the reporting period in the aggregate value (measured at the lower of net carrying value or fair value less cost of disposal) for assets of a disposal group, including a component of the entity (discontinued operation), to be sold or that has subsequently been disposed of through sale, as of the financial statement date, and the carrying value of obligations relating to the sale, disposal or planned sale in the near future (generally within one year) of a disposal group, including a component of the entity (discontinued operation), as of the balance sheet date.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FinancialInstrumentsOwnedAtFairValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_FairValueAssetsMeasuredOnRecurringBasisGainLossIncludedInCostOfGoodsSold">
    <definition>Fair Value Assets Measured On Recurring Basis Gain Loss Included In Cost Of Goods Sold</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchasesSalesIssuancesSettlements">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherIncomeAndOtherExpenseDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_IncreaseDecreaseInTaxesPayable">
    <definition>The net change during the period in the amount of obligations incurred and payable for statutory income, sales, use, payroll, excise, real, property and other taxes.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InterestExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_AggregatePurchaseSublimit">
    <definition>Aggregate Purchase Sublimit</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ChargeRelatedToEcAnnouncement">
    <definition>Charge Related To EC Announcement</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_DiscreteIncomeTaxChargeForInterestPaidToInternalRevenueServiceOnPreviouslyDeferredGain">
    <definition>Discrete Income Tax Charge For Interest Paid To The Internal Revenue Service On A Previously Deferred Gain</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SegmentReportingDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeTaxReconciliationTaxContingenciesForeign">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_SegmentReportingInformationRevenueFromExternalCustomersTotal">
    <definition>Segment Reporting Information Revenue From External Customers Total</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetCashProvidedByUsedInFinancingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_SegmentReportingInformationIntersegmentRevenueTotal">
    <definition>Segment Reporting Information Intersegment Revenue Total</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeAvailableForSaleSecuritiesAdjustmentNetOfTaxPeriodIncreaseDecrease">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RevenueRecognitionPolicyTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_BusinessExitCosts">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_SegmentReportingInformationImpactOfLifo">
    <definition>Segment Reporting Information Impact Of Lifo</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LiabilitiesAndStockholdersEquity">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetIncomeLoss">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SalesRevenueGoodsNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EarningsPerShareTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_FairValuesOfOutstandingDerivativeContractsRecordedAsAssetsTextBlock">
    <definition>The fair values of outstanding derivative contracts recorded as assets [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_TradingSymbol">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ScheduleOfEarningsPerShareBasicAndDilutedByCommonClassTableTextBlock">
    <definition>Disclosure of the description and amount of each reconciling item used to derive the numerator and denominator for the calculation of an entity's basic and diluted earnings per share.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherAssetsCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_PreferredStockDividendsPerShareDeclared">
    <definition>Aggregate dividends declared during the period for each share of preferred stock outstanding.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPensionPlanLiabilitiesNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_PercentageOfGoodwillImpairmentExistsBasedOnQualitativeFactorsMinimum">
    <definition>Percentage of Goodwill Impairment Exists Based On Qualitative Factors Minimum</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_RecommendedCappingRemedyMax">
    <definition>Recommended Capping Remedy Max</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInInventories">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherInventoryNetOfReserves">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DisposalGroupIncludingDiscontinuedOperationInventory">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PreferredStockValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NonoperatingIncomeExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RepaymentsOfLongTermDebt">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DisposalGroupIncludingDiscontinuedOperationAccruedLiabilities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StockIssuedDuringPeriodValueNewIssues">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_BasisOfPresentationAndSignificantAccountingPoliciesTextBlock">
    <definition>The entire disclosure for the basis of presentation, or accounting, and significant accounting policies.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ForeignCurrencyTransactionGainLossAfterTax">
    <definition>Foreign Currency Transaction Gain Loss After Tax</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_StockIssuedDuringPeriodSharesPeriodParValue">
    <definition>Stock Issued During Period Shares Period Par Value</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeReclassificationAdjustmentOnDerivativesIncludedInNetIncomeNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_InvestmentInEquityAffiliates">
    <definition>Investment In Equity Affiliates</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RestructuringReserveAccrualAdjustment">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_WeightedAverageCostInventoryAmount">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_EquityInvestmentPercentageOwnershipAcquired">
    <definition>Equity Investment Percentage Ownership Acquired</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DebtInstrumentConvertibleInterestExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherLiabilitiesCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PropertyPlantAndEquipmentNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherAssetImpairmentCharges">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RestructuringReserveSettledWithCash">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_AluminumFuturesDesignatedAsFairValueHedgesInKmt">
    <definition>Aluminum Futures Designated As Fair Value Hedges, In KMT</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_AmountInvestedUnderProjectFinancing">
    <definition>Amount Invested Under Project Financing</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_FairValueMeasurementPolicyTextBlock">
    <definition>Fair Value Measurement Policy [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeLossFromContinuingOperationsPerBasicShare">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ScheduleOfSegmentReportingInformationToConsolidateNetIncomeLossAttributableToParentTextBlock">
    <definition>Schedule Of Segment Reporting Information To Consolidate Net Income Loss Attributable To Parent [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_Goodwill">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_NumberOfEmployeesAssociatedWithLayoffCosts">
    <definition>The number of employees an entity expects to layoff that correlates to the layoff charges recorded during the period.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInReceivables">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DisposalGroupsIncludingDiscontinuedOperationsDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_Outstandingforwardcontractsenteredintoashedgingforecastedtransactionsmeasuredinkmt">
    <definition>Outstanding Forward Contracts Entered Into As Hedging Forecasted Transactions Measured In Kmt</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsOfDividendsCommonStock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeFairValueOfDerivativeLiability">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EquityMethodInvestments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_OwnershipInterestInJointVentureAtFairMarketValue">
    <definition>Ownership Interest in Joint Venture at Fair Market Value</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_GainLossOnSaleOfOtherAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_SegmentReportingInformationNetIncomeLossAttributableToNoncontrollingInterest">
    <definition>Segment Reporting Information Net Income Loss Attributable To Noncontrolling Interest</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DividendsPreferredStockCash">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_TotalCostsAndExpenses">
    <definition>The net total of all costs and expenses associated with normal operations and income and expenses associated with nonoperating activities, including interest and debt-related expenses.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_SegmentReportingInformationInterestExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermDebtAndCapitalLeaseObligationsCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanAmortizationOfPriorServiceCostCredit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProfitLoss">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_IncreaseInEstimatedCostToCompleteEstreitoProject">
    <definition>Increase In Estimated Cost To Complete Esteito Project</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_AcquisitionsAndDispositionsDisclosureTextBlock">
    <definition>This element may be used to capture disclosure pertaining to acquisitions and dispositions. For acquisitions, description of a business acquisition (or series of individually immaterial business combinations) planned, initiated, or completed during the period, including background, timing, and allocation of acquisition costs. For dispositions, disclosure includes the facts and circumstances leading to the completed or expected disposal, manner and timing of disposal, the gain or loss recognized in the income statement and the income statement caption that includes that gain or loss, and the segment in which the disposal group was reported.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_DocumentFiscalYearFocus">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_TotalShareOfEstreitoProject">
    <definition>Total Share Of Estreito Project</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DebtInstrumentFaceAmount">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StockholdersEquity">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_CapitalInvestmentOverYear">
    <definition>Capital Investment, Over Year</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherNonoperatingIncomeExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ScheduleOfProFormaRestructuringChargesByReportableSegmentBeforeIncomeTaxTextBlock">
    <definition>An entity's restructuring charges before income tax by reportable segment had such charges been included in the entity's segment results.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermDebt">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherRestructuringCosts">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PartnersCapitalAccountReturnOfCapital">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfDisposalGroupsIncludingDiscontinuedOperationsIncomeStatementBalanceSheetAndAdditionalDisclosuresTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AdditionalPaidInCapital">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherPostretirementDefinedBenefitPlanLiabilitiesNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_AmendmentFlag">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InvestmentIncomeInterest">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_Liabilities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_IncomeLossFromContinuingOperationsAvailableToCommonShareholdersDiluted">
    <definition>Income Loss From Continuing Operations Available To Common Shareholders - Diluted</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeInstrumentsGainLossReclassifiedFromAccumulatedOCIIntoIncomeEffectivePortionNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DebtInstrumentInterestRateStatedPercentage">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ItalianGovernmentExtendedTariffChargeMax">
    <definition>Italian Government extended tariff charge max</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_PreferredAndCommonStockTextBlock">
    <definition>Preferred and Common Stock [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_TotalShareOfSerradoFacao">
    <definition>Total Share Of Serrado Facao</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockSharesAuthorized">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromIssuanceOfLongTermDebt">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ItalianGovernmentExtendedTariffChargeMin">
    <definition>Italian Government extended tariff charge min</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_DiscreteIncomeTaxChargeForChangeInAnticipatedStructureOfPotentialSale">
    <definition>Discrete Income Tax Charge For A Change In The Anticipated Structure Of Potential Sale</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DisposalGroupIncludingDiscontinuedOperationPropertyPlantAndEquipmentNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsToAcquireInvestments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_AmountContributedTowardCommitment">
    <definition>Amount contributed toward commitment</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetCashProvidedByUsedInOperatingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_SegmentreportinginformationequityInNetincomeOfEquityMethodInvesteesOfSegmentTotal">
    <definition>Equity In Net Income Of Equity Method Investees Of Segment Total</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ScheduleOfSubsequentEventsTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_DisposalGroupNotDiscontinuedOperationAdditionalInformation">
    <definition>Additional financial information of a disposal group, not classified as discontinued operations, from last annual period prior to divestiture, such as amount of sales , net income or loss, etc.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EffectiveIncomeTaxRateContinuingOperations">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_StockIssuedDuringPeriodSharesNewIssues">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_CapitalInvestmentCommitmentPaidInPeriod">
    <definition>CapitalInvestmentCommitmentPaidToDate</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_CurrentFiscalYearEndDate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_TransfersAndServicingOfFinancialAssetsTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_TotalInvestmentInEsteirtoProject">
    <definition>Total Investment In Esteirto Project</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_FairValueGainsAndLossesOnDerivativesContractsTextBlock">
    <definition>The fair value gains and losses on derivatives contracts [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_NetCashProvidedByUsedInInvestingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPeriodIncreaseDecrease">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSalesIncreaseDecrease">
    <definition>Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Sales Increase Decrease</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DisposalGroupIncludingDiscontinuedOperationOtherAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InventoryDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_EnvironmentalLossContingenciesAdjustment">
    <definition>Environmental Loss Contingencies Adjustment</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_MinimumamountOfCashPaymentsExpectedToBePaidBeyondCurrentAnnualPeriod">
    <definition>The minimum amount of  cash payments expected to be paid beyond the end of the current annual period related to restructuring charges such as ongoing site remediation work, special termination benefit payments, least termination costs, among others.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PropertyPlantAndEquipmentGross">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeLossFromEquityMethodInvestments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_PercentageOfCostOfGoodsSold">
    <definition>Percentage of cost of goods sold</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInAccruedLiabilities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_FairValueAssetsMeasuredOnRecurringBasisGainLossIncludedInSales">
    <definition>Fair Value Assets Measured On Recurring Basis Gain Loss Included In Sales</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ShareBasedCompensation">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_FairValueAssetsMeasuredOnRecurringBasisGainLossIncludedInOtherExpenses">
    <definition>Fair Value Assets Measured On Recurring Basis Gain Loss Included In Other Expenses</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LossContingencyRangeOfPossibleLossMaximum">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeTaxReconciliationOtherReconcilingItems">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CashFlowHedgeGainLossToBeReclassifiedWithinTwelveMonths">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_OwnershipInterestIssuedAsGuaranteeForSmeltingAndRolingCompanies">
    <definition>Ownership Interest Issued As Guarantee For Smelting And Roling Companies</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_DocumentType">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_BusinessAcquisitionCostOfAcquiredEntityPurchasePrice">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_MinorityInterestDecreaseFromRedemptions">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_GainOrLossOnHedgedItemsTextBlock">
    <definition>Gain or loss on hedged items [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_NonvestedSharesWithForfeitableDividends">
    <definition>This element represents the number of outstanding nonvested stock awards that contain forfeitable rights to dividends or dividend equivalents (whether paid or unpaid).</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AssetsCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_MaximumAmountOfCashPaymentsExpectedToBePaidBeyondCurrentAnnualPeriod">
    <definition>The maximum amount of  cash payments expected to be paid beyond the end of the current annual period related to restructuring charges such as ongoing site remediation work, special termination benefit payments, least termination costs, among others.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetOtherExpenses">
    <definition>Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Other Expenses</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeTaxExpenseBenefit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ScheduleOfMajorClassesOfAssetsAndLiabilitiesOfOperationsHeldForSaleTextBlock">
    <definition>Schedule Of Major Classes Of Assets And Liabilities Of Operations Held For Sale [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanExpectedReturnOnPlanAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_AssetsHeldForSale">
    <definition>The aggregate value (measured at the lower of net carrying value or fair value less cost of disposal) for assets of a disposal group, including a component of the entity (discontinued operation), to be sold or that has subsequently been disposed of through sale, as of the financial statement date.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeTaxDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InventoryNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EarningsPerShareBasic">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_IncomeLossFromContinuingOperationsAvailableToCommonEquity">
    <definition>Income or loss from continuing operations after adjustments for dividends on preferred stock (declared in the period) and/or cumulative preferred stock (accumulated for the period).</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_CashAvailableForPurchaseOfDebt">
    <definition>Cash Available For Purchase of Debt</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeFairValueOfDerivativeAsset">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInOtherComprehensiveIncome">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_StockIssuedDuringPeriodValue">
    <definition>Stock Issued During Period, Value</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RestructuringReservePeriodExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_GainsAndLossesOnDerivativesTextBlock">
    <definition>Gains and losses on derivatives [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ExpansionOfProductionPlanIncludedInAssetImpairment">
    <definition>Expansion Of Production Plan Included In Asset Impairment</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncrementalCommonSharesAttributableToConversionOfDebtSecurities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_OutstandingForwardContractsThatWereEnteredIntoToHedgeForwardTransactionsTextBlock">
    <definition>Outstanding forward contracts that were entered into to hedge forward transactions [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ResearchAndDevelopmentExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanServiceCost">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DefinedBenefitPlanAmortizationOfGainsLosses">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ReductionInProductionDueToMarketCondition">
    <definition>Reduction In Production Due To Market Condition</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_PremiumToBePaidForPurchasePerBaseOfNote">
    <definition>Premium To Be Paid For Purchase Per Base of Note</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherAssetsNoncurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockSharesIssued">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_MinorityInterest">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RestructuringReserve">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PercentageOfLIFOInventory">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_DocumentPeriodEndDate">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DerivativeInstrumentsGainLossRecognizedInIncomeIneffectivePortionAndAmountExcludedFromEffectivenessTestingNet">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_BusinessCombinationsAndOtherPurchaseOfBusinessTransactionsPolicyTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DividendsCommonStockCash">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_RestructuringAndOtherCharges">
    <definition>Amount charged against earnings in the period for incurred and estimated costs associated with exit from or disposal of business activities or restructurings pursuant to a program that is planned and controlled by management, and materially changes either the scope of a business undertaken by an entity, or the manner in which that business is conducted.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockDividendsPerShareCashPaid">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermDebtAndCapitalLeaseObligations">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_GainLossOnDispositionOfAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsToAcquireAdditionalInterestInSubsidiaries">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityRegistrantName">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommitmentsFairValueDisclosure">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_SegmentReportingInformationIncomeTaxExpenseBenefitTotal">
    <definition>Segment Reporting Information Income Tax Expense Benefit Total</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_ProceedsFromSaleMaturityAndCollectionsOfInvestments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ContributedAmountToSerraDoFacao">
    <definition>Contributed Amount to Serra do Facao</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_OtherExitCostsAfterTaxAndNoncontrollingInterests">
    <definition>Other Exit Costs, After Tax And Noncontrolling Interests</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_GuaranteeObligationsCurrentCarryingValue">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_DerivativeInstrumentsAndHedgingActivitiesAndFairValueDisclosuresTextBlock">
    <definition>This element can be used to disclose the entity's entire derivative instruments and hedging activities disclosure as a single block of text. Describes an entity's risk management strategies, derivatives in hedging activities and non-hedging derivative instruments, the assets, obligations, liabilities, revenues and expenses arising there from, and the amounts of and methodologies and assumptions used in determining the amounts of such items. This item also represents the complete disclosure regarding the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments, assets, and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the Company is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risk is are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ScheduleOfRestructuringReserveByTypeOfRestructuringTextBlock">
    <definition>Schedule Of Restructuring Reserve By Type Of Restructuring Text Block</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LitigationSettlementExpense">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_DebtInstrumentPeriodicPaymentInterest">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PensionContributions">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EmployeeRelatedLiabilitiesCurrent">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_DividendsAndAllocationOfUndistributedEarningsToParticipatingSecurities">
    <definition>Amount of dividends paid to participating securities (unvested awards) on a basis equivalent to holders of an entity's common stock plus an allocation of the undistributed earnings of an entity to the participating securities on the same basis as the paid dividends.  This deduction in the EPS reconciliation is only applicable in periods when an entity generates income as the holders of the participating securities do not share in the losses of an entity unlike a common shareholder.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_EquityMethodInvestmentOwnershipPercentage">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_WriteOffOfReceivable">
    <definition>Write-off of Receivable</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_CarryingValuesAndFairValuesOfAlcoaSOtherFinancialInstrumentsTextBlock">
    <definition>Carrying values and fair values of Alcoa's other financial instruments [Text Block]</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_InventorySuppliesNetOfReserves">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RetainedEarningsAccumulatedDeficit">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_CapitalContribution">
    <definition>Capital Contribution</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncreaseDecreaseInOtherOperatingAssets">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_LiabilitiesOfOperationsHeldForSale">
    <definition>Carrying value of obligations relating to the sale, disposal or planned sale in the near future (generally within one year) of a disposal group, including a component of the entity (discontinued operation), as of the balance sheet date.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_RestructuringAndRelatedActivitiesDisclosureTextBlock">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesOther">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_TotalSegmentAtoi">
    <definition>Total Segment Atoi</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_InventoryWriteDownAfterTaxAndNonControllingInterests">
    <definition>Inventory Write Down, After Tax And Non-Controlling Interests</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_BaseForConsiderationAndPremium">
    <definition>Base For Consideration and Premium</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_PaymentsOfDistributionsToAffiliates">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_AdditionalAcquiredShares">
    <definition>Additional acquired shares</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_EntityCommonStockSharesOutstanding">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="dei_DocumentFiscalPeriodFocus">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_ParticipatingNonvestedSharesWithNonForfeitableDividendRights">
    <definition>This element represents the number of outstanding nonvested stock awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid).</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockSharesHeldInEmployeeTrust">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_OtherComprehensiveIncomeDefinedBenefitPlansAdjustmentNetOfTaxPeriodIncreaseDecrease">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_CommonStockSharesOutstanding">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="aa_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetCostOfGoodsSold">
    <definition>Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset Cost Of Goods Sold</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_LongTermInvestments">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
  <Element Id="us-gaap_IncomeLossFromContinuingOperationsIncludingPortionAttributableToNoncontrollingInterest">
    <definition>No authoritative reference available.</definition>
    <reference>No authoritative reference available.</reference>
  </Element>
</DefinitionAndReference>
