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Income Taxes - Additional Information (Detail) (USD $) | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Income Tax Contingency [Line Items] |  |
Effective tax rate | 47.00%us-gaap_EffectiveIncomeTaxRateContinuingOperations | 28.10%us-gaap_EffectiveIncomeTaxRateContinuingOperations
Income tax benefit recognized | 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate | 35.00%us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate
Income tax benefit recognized | $ 226,000,000 us-gaap_IncomeTaxExpenseBenefit | $ (77,000,000)us-gaap_IncomeTaxExpenseBenefit
Operational losses in certain foreign jurisdictions | 35,000,000 aa_IncomeTaxReconciliationNondeductibleExpenseInForeignJurisdictions | 56,000,000 aa_IncomeTaxReconciliationNondeductibleExpenseInForeignJurisdictions
Russia [Member] |  |
Income Tax Contingency [Line Items] |  |
Income tax benefit recognized | 0 us-gaap_IncomeTaxExpenseBenefit / us-gaap_StatementGeographicalAxis = country_RU |
Alcoa World Alumina and Chemicals [Member] |  |
Income Tax Contingency [Line Items] |  |
Discrete income tax charge | 83,000,000 aa_IncomeTaxReconciliationChangeInEnactedTaxRateTaxExpense / us-gaap_OtherOwnershipInterestsByNameAxis = aa_AlcoaWorldAluminaAndChemicalsMember |
Alcoa [Member] | Alcoa World Alumina and Chemicals [Member] |  |
Income Tax Contingency [Line Items] |  |
Percent of equity investment in other entity | 60.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_OtherOwnershipInterestsByNameAxis = aa_AlcoaWorldAluminaAndChemicalsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = us-gaap_ParentCompanyMember |
Deferred tax liability | 50,000,000 us-gaap_DeferredIncomeTaxLiabilities / us-gaap_OtherOwnershipInterestsByNameAxis = aa_AlcoaWorldAluminaAndChemicalsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = us-gaap_ParentCompanyMember |
Deferred tax asset written off as valuation allowance | 60.00%aa_PercentageOfDeferredTaxAssetsValuationAllowance / us-gaap_OtherOwnershipInterestsByNameAxis = aa_AlcoaWorldAluminaAndChemicalsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = us-gaap_ParentCompanyMember |
Alumina Limited [Member] | Alcoa World Alumina and Chemicals [Member] |  |
Income Tax Contingency [Line Items] |  |
Percent of equity investment in other entity | 40.00%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_OtherOwnershipInterestsByNameAxis = aa_AlcoaWorldAluminaAndChemicalsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_AluminaLimitedMember |
Foreign Jurisdictions [Member] |  |
Income Tax Contingency [Line Items] |  |
Income tax benefit recognized | 0 us-gaap_IncomeTaxExpenseBenefit / us-gaap_IncomeTaxAuthorityAxis = aa_ForeignJurisdictionsMember | 0 us-gaap_IncomeTaxExpenseBenefit / us-gaap_IncomeTaxAuthorityAxis = aa_ForeignJurisdictionsMember
United States [Member] |  |
Income Tax Contingency [Line Items] |  |
Discrete income tax benefit | $ 33,000,000 aa_IncomeTaxReconciliationChangeInEnactedTaxRateTaxBenefit / us-gaap_IncomeTaxAuthorityAxis = country_US |

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