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Contingencies and Commitments - Additional Information - 2 (Detail) | 3 Months Ended |  |  |  | 3 Months Ended |  |  |  | 3 Months Ended |  |  | 3 Months Ended | 0 Months Ended | 3 Months Ended | 1 Months Ended | 0 Months Ended | 1 Months Ended | 0 Months Ended |  | 36 Months Ended |  | 3 Months Ended |  | 3 Months Ended | 12 Months Ended | 1 Months Ended | 12 Months Ended | 93 Months Ended | 3 Months Ended | 12 Months Ended | 3 Months Ended
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Mar. 31, 2015 USD ($) | Mar. 31, 2015 EUR (€) | Jun. 12, 2012 USD ($) | Jun. 12, 2012 EUR (€) | Mar. 31, 2015 State and Local Jurisdiction [Member] USD ($) | Mar. 31, 2015 State and Local Jurisdiction [Member] BRL | Mar. 31, 2015 Maaden Alcoa Joint Venture [Member] USD ($) Entity | Mar. 31, 2015 Maaden Alcoa Joint Venture [Member] SAR | Dec. 31, 2014 Maaden Alcoa Joint Venture [Member] USD ($) | Mar. 31, 2015 Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] USD ($) | Mar. 31, 2015 Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] Other Noncurrent Liabilities and Deferred Credits [Member] USD ($) | Dec. 31, 2014 Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] Other Noncurrent Liabilities and Deferred Credits [Member] USD ($) | Mar. 31, 2015 Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] Financial Guarantee [Member] USD ($) | Mar. 31, 2015 Maaden Alcoa Joint Venture Mine And Refinery Company [Member] USD ($) | Mar. 31, 2015 Maaden Alcoa Joint Venture Mine And Refinery Company [Member] Other Noncurrent Liabilities and Deferred Credits [Member] USD ($) | Dec. 31, 2014 Maaden Alcoa Joint Venture Mine And Refinery Company [Member] Other Noncurrent Liabilities and Deferred Credits [Member] USD ($) | Mar. 31, 2015 Maaden Alcoa Joint Venture Mine And Refinery Company [Member] Financial Guarantee [Member] USD ($) | Feb. 27, 2014 Ligestra [Member] USD ($) | Feb. 27, 2014 Ligestra [Member] EUR (€) | Mar. 31, 2015 Ligestra [Member] | Jan. 31, 2014 Ligestra [Member] Minimum [Member] | Jan. 31, 2014 Ligestra [Member] Maximum [Member] | Feb. 27, 2014 Italian Ministry of Environment and Protection of Land and Sea[Member] USD ($) | Feb. 27, 2014 Italian Ministry of Environment and Protection of Land and Sea[Member] EUR (€) | Apr. 08, 2013 Alcoa World Alumina Brasil [Member] BRL | Mar. 31, 2013 Alcoa World Alumina Brasil [Member] USD ($) | Mar. 31, 2013 Alcoa World Alumina Brasil [Member] BRL | May 31, 2012 Alcoa World Alumina Brasil [Member] USD ($) | May 31, 2012 Alcoa World Alumina Brasil [Member] BRL | Apr. 08, 2013 Alcoa World Alumina Brasil [Member] Minimum [Member] USD ($) | Apr. 08, 2013 Alcoa World Alumina Brasil [Member] Maximum [Member] USD ($) | Apr. 08, 2013 Alcoa World Alumina Brasil [Member] Fixed Assets [Member] BRL | Apr. 08, 2013 Alcoa World Alumina Brasil [Member] Fixed Assets [Member] Minimum [Member] USD ($) | Apr. 08, 2013 Alcoa World Alumina Brasil [Member] Fixed Assets [Member] Maximum [Member] USD ($) | Dec. 31, 2002 Alcoa Aluminio [Member] t | Mar. 31, 2015 Maaden Company [Member] Maaden Alcoa Joint Venture [Member] | Mar. 31, 2015 Alcoa [Member] Maaden Alcoa Joint Venture [Member] USD ($) | Mar. 31, 2015 Alcoa [Member] Maaden Alcoa Joint Venture Smelter And Rolling Mill Companies [Member] USD ($) | Mar. 31, 2015 Alcoa [Member] Maaden Alcoa Joint Venture Mine And Refinery Company [Member] USD ($) | Mar. 31, 2015 Estreito Project [Member] USD ($) MWh | Mar. 31, 2015 Estreito Project [Member] BRL | Dec. 31, 2014 Portovesme [Member] USD ($) | Dec. 31, 2009 Portovesme [Member] USD ($) | Dec. 31, 2012 Baie Comeau [Member] USD ($) | Dec. 31, 2012 Mosjoen [Member] USD ($) | Oct. 31, 2013 Fusina [Member] USD ($) | Dec. 31, 2009 Fusina [Member] USD ($) | Dec. 31, 2004 Dampier to Bunbury Natural Gas Pipeline [Member] USD ($) | Dec. 31, 2004 Dampier to Bunbury Natural Gas Pipeline [Member] AUD | Sep. 30, 2011 Dampier to Bunbury Natural Gas Pipeline [Member] USD ($) | Sep. 30, 2011 Dampier to Bunbury Natural Gas Pipeline [Member] AUD | Mar. 31, 2015 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] USD ($) | Mar. 31, 2015 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] AUD | Dec. 31, 2014 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] USD ($) | Dec. 31, 2014 Dampier to Bunbury Natural Gas Pipeline [Member] Three-Year Equity Call Plan [Member] AUD | Mar. 31, 2015 Dampier to Bunbury Natural Gas Pipeline [Member] New Equity Call Plan [Member] USD ($) | Mar. 31, 2015 Dampier to Bunbury Natural Gas Pipeline [Member] New Equity Call Plan [Member] AUD
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase in remediation reserve |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 3,000,000 us-gaap_AccrualForEnvironmentalLossContingenciesPeriodIncreaseDecrease / us-gaap_StatementGeographicalAxis = aa_PortovesmeSiteMember | $ 3,000,000 us-gaap_AccrualForEnvironmentalLossContingenciesPeriodIncreaseDecrease / us-gaap_StatementGeographicalAxis = aa_PortovesmeSiteMember | $ 25,000,000 us-gaap_AccrualForEnvironmentalLossContingenciesPeriodIncreaseDecrease / us-gaap_StatementGeographicalAxis = aa_BaieComeauQuebecCanadaMember | $ 20,000,000 us-gaap_AccrualForEnvironmentalLossContingenciesPeriodIncreaseDecrease / us-gaap_StatementGeographicalAxis = aa_MosjoenMember | $ 0 us-gaap_AccrualForEnvironmentalLossContingenciesPeriodIncreaseDecrease / us-gaap_StatementGeographicalAxis = aa_FusinaSiteMember | $ 12,000,000 us-gaap_AccrualForEnvironmentalLossContingenciesPeriodIncreaseDecrease / us-gaap_StatementGeographicalAxis = aa_FusinaSiteMember |  |  |  |  |  |  |  |  |  |
Percentage of payments and remediation costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50.00%aa_PercentageOfPaymentsAndRemediationCostsUnderAdministrativeAgreement / dei_LegalEntityAxis = aa_LigestraMember / us-gaap_RangeAxis = us-gaap_MinimumMember | 80.00%aa_PercentageOfPaymentsAndRemediationCostsUnderAdministrativeAgreement / dei_LegalEntityAxis = aa_LigestraMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Soil remediation project, estimated cost |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 33,000,000 us-gaap_CostOfServicesEnvironmentalRemediation / dei_LegalEntityAxis = aa_ItalianMinistryOfEnvironmentAndProtectionOfLandAndSeaMember | 24,000,000 us-gaap_CostOfServicesEnvironmentalRemediation / dei_LegalEntityAxis = aa_ItalianMinistryOfEnvironmentAndProtectionOfLandAndSeaMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payments for emergency action and natural resource damages |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25,000,000 aa_EnvironmentalRemediationPaymentsForEmergencyActionAndNaturalResourcesDamages / dei_LegalEntityAxis = aa_ItalianMinistryOfEnvironmentAndProtectionOfLandAndSeaMember | 18,000,000 aa_EnvironmentalRemediationPaymentsForEmergencyActionAndNaturalResourcesDamages / dei_LegalEntityAxis = aa_ItalianMinistryOfEnvironmentAndProtectionOfLandAndSeaMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Costs and payments |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 17,000,000 aa_EnvironmentalRemediationCostsAndPayments / dei_LegalEntityAxis = aa_LigestraMember | 12,000,000 aa_EnvironmentalRemediationCostsAndPayments / dei_LegalEntityAxis = aa_LigestraMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Costs and payments related to damages |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 9,000,000 aa_EnvironmentalRemediationDamages / dei_LegalEntityAxis = aa_LigestraMember | 6,000,000 aa_EnvironmentalRemediationDamages / dei_LegalEntityAxis = aa_LigestraMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Payment period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revised project cost submitted to reflect the removal of a larger volume of contaminated soil | 7,000,000 us-gaap_AccrualForEnvironmentalLossContingenciesIncreaseDecreaseForRevisionInEstimates |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total combined assessments | 247,000,000 aa_IncomeTaxExaminationAssessmentOutstanding | 228,000,000 aa_IncomeTaxExaminationAssessmentOutstanding |  |  | 40,000,000 aa_IncomeTaxExaminationAssessmentOutstanding / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember | 130,000,000 aa_IncomeTaxExaminationAssessmentOutstanding / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Disallowed tax credits |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 110,000,000 aa_TaxCreditPreviouslyClaimedAndDisallowedByTaxAuthority / dei_LegalEntityAxis = aa_AlcoaWorldAluminaBrasilMember | 220,000,000 aa_TaxCreditPreviouslyClaimedAndDisallowedByTaxAuthority / dei_LegalEntityAxis = aa_AlcoaWorldAluminaBrasilMember |  |  |  |  | 175,000,000 aa_TaxCreditPreviouslyClaimedAndDisallowedByTaxAuthority / dei_LegalEntityAxis = aa_AlcoaWorldAluminaBrasilMember / us-gaap_PropertyPlantAndEquipmentByTypeAxis = aa_FixedAssetsMember | 0 aa_TaxCreditPreviouslyClaimedAndDisallowedByTaxAuthority / dei_LegalEntityAxis = aa_AlcoaWorldAluminaBrasilMember / us-gaap_PropertyPlantAndEquipmentByTypeAxis = aa_FixedAssetsMember / us-gaap_RangeAxis = us-gaap_MinimumMember | 55,000,000 aa_TaxCreditPreviouslyClaimedAndDisallowedByTaxAuthority / dei_LegalEntityAxis = aa_AlcoaWorldAluminaBrasilMember / us-gaap_PropertyPlantAndEquipmentByTypeAxis = aa_FixedAssetsMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of penalty of the gross disallowed amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 50.00%aa_PercentageOfPenaltyOnAmountOfAdditionalTaxesDue / dei_LegalEntityAxis = aa_AlcoaWorldAluminaBrasilMember | 50.00%aa_PercentageOfPenaltyOnAmountOfAdditionalTaxesDue / dei_LegalEntityAxis = aa_AlcoaWorldAluminaBrasilMember | 50.00%aa_PercentageOfPenaltyOnAmountOfAdditionalTaxesDue / dei_LegalEntityAxis = aa_AlcoaWorldAluminaBrasilMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Value added tax receivable |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 41,000,000 us-gaap_IncomeTaxCreditsAndAdjustments / dei_LegalEntityAxis = aa_AlcoaWorldAluminaBrasilMember | 82,000,000 us-gaap_IncomeTaxCreditsAndAdjustments / dei_LegalEntityAxis = aa_AlcoaWorldAluminaBrasilMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated range of reasonably possible loss, minimum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 155,000,000 us-gaap_IncomeTaxExaminationEstimateOfPossibleLoss / dei_LegalEntityAxis = aa_AlcoaWorldAluminaBrasilMember |  |  |  |  | 0 us-gaap_IncomeTaxExaminationEstimateOfPossibleLoss / dei_LegalEntityAxis = aa_AlcoaWorldAluminaBrasilMember / us-gaap_RangeAxis = us-gaap_MinimumMember | 50,000,000 us-gaap_IncomeTaxExaminationEstimateOfPossibleLoss / dei_LegalEntityAxis = aa_AlcoaWorldAluminaBrasilMember / us-gaap_RangeAxis = us-gaap_MaximumMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Administrative appeal, assessment period |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Metal sold per month |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,000 aa_AluminumSoldInMetricTonPerMonthByFacility / dei_LegalEntityAxis = aa_AlcoaAluminoMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest issued as guarantee for Saudi Arabian Joint Venture |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 74.90%aa_OwnershipPercentage / invest_InvestmentIssuerAxis = aa_MaadenAlcoaJointVentureMember / dei_LegalEntityAxis = aa_MaadenCompanyMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership interest issued as guarantee for Saudi Arabian Joint Venture |  |  |  |  |  |  | 25.10%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMember | 25.10%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of companies in Saudi Arabian joint venture |  |  |  |  |  |  | 3 aa_NumberOfCompaniesInJointVenture / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMember | 3 aa_NumberOfCompaniesInJointVenture / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amount invested by Alcoa and Aluminum Financing Limited |  |  |  |  |  |  | 10,800,000,000 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMember | 40,500,000,000 us-gaap_LongTermPurchaseCommitmentAmount / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,100,000,000 us-gaap_LongTermPurchaseCommitmentAmount / dei_LegalEntityAxis = us-gaap_ParentCompanyMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 39,000,000 us-gaap_LongTermPurchaseCommitmentAmount / invest_InvestmentAxis = aa_ThreeYearEquityCallPlanMember / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember | 40,000,000 us-gaap_LongTermPurchaseCommitmentAmount / invest_InvestmentAxis = aa_ThreeYearEquityCallPlanMember / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember | 30,000,000 us-gaap_LongTermPurchaseCommitmentAmount / invest_InvestmentAxis = aa_NewEquityCallPlanMember / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember | 36,000,000 us-gaap_LongTermPurchaseCommitmentAmount / invest_InvestmentAxis = aa_NewEquityCallPlanMember / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember
Capital investment |  |  |  |  |  |  | 4,000,000 us-gaap_PaymentsToAcquireEquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 956,000,000 us-gaap_PaymentsToAcquireEquityMethodInvestments / dei_LegalEntityAxis = us-gaap_ParentCompanyMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMember |  |  |  |  |  |  |  |  |  |  | 17,000,000 us-gaap_PaymentsToAcquireEquityMethodInvestments / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember | 24,000,000 us-gaap_PaymentsToAcquireEquityMethodInvestments / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember | 141,000,000 us-gaap_PaymentsToAcquireEquityMethodInvestments / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember | 176,000,000 us-gaap_PaymentsToAcquireEquityMethodInvestments / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember | 3,000,000 us-gaap_PaymentsToAcquireEquityMethodInvestments / invest_InvestmentAxis = aa_ThreeYearEquityCallPlanMember / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember | 5,000,000 us-gaap_PaymentsToAcquireEquityMethodInvestments / invest_InvestmentAxis = aa_ThreeYearEquityCallPlanMember / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember |  |  | 4,000,000 us-gaap_PaymentsToAcquireEquityMethodInvestments / invest_InvestmentAxis = aa_NewEquityCallPlanMember / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember | 6,000,000 us-gaap_PaymentsToAcquireEquityMethodInvestments / invest_InvestmentAxis = aa_NewEquityCallPlanMember / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember
Equity method investment, carrying value |  |  |  |  |  |  | 969,000,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMember |  | 983,000,000 us-gaap_EquityMethodInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Capital investment |  |  |  |  |  |  |  |  |  | 1,133,000,000 us-gaap_CapitalizationLongtermDebtAndEquity / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureSmelterAndRollingMillCompaniesMember |  |  |  | 560,000,000 us-gaap_CapitalizationLongtermDebtAndEquity / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMineAndRefineryCompanyMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4,515,000,000 us-gaap_CapitalizationLongtermDebtAndEquity / dei_LegalEntityAxis = us-gaap_ParentCompanyMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureSmelterAndRollingMillCompaniesMember | 2,232,000,000 us-gaap_CapitalizationLongtermDebtAndEquity / dei_LegalEntityAxis = us-gaap_ParentCompanyMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMineAndRefineryCompanyMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt service requirements, principal |  |  |  |  |  |  |  |  |  |  |  |  | 176,000,000 us-gaap_DebtInstrumentPeriodicPaymentPrincipal / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_FinancialGuaranteeMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureSmelterAndRollingMillCompaniesMember |  |  |  | 120,000,000 us-gaap_DebtInstrumentPeriodicPaymentPrincipal / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_FinancialGuaranteeMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMineAndRefineryCompanyMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt service requirements, interest maximum |  |  |  |  |  |  |  |  |  |  |  |  | 60,000,000 us-gaap_DebtInstrumentPeriodicPaymentInterest / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_FinancialGuaranteeMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureSmelterAndRollingMillCompaniesMember |  |  |  | 30,000,000 us-gaap_DebtInstrumentPeriodicPaymentInterest / us-gaap_GuaranteeObligationsByNatureAxis = us-gaap_FinancialGuaranteeMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMineAndRefineryCompanyMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Guarantee issued on behalf of smelting and rolling mill companies |  |  |  |  |  |  |  |  |  |  | 8,000,000 us-gaap_GuaranteeObligationsCurrentCarryingValue / us-gaap_BalanceSheetLocationAxis = aa_OtherNoncurrentLiabilitiesAndDeferredCreditsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureSmelterAndRollingMillCompaniesMember | 8,000,000 us-gaap_GuaranteeObligationsCurrentCarryingValue / us-gaap_BalanceSheetLocationAxis = aa_OtherNoncurrentLiabilitiesAndDeferredCreditsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureSmelterAndRollingMillCompaniesMember |  |  | 4,000,000 us-gaap_GuaranteeObligationsCurrentCarryingValue / us-gaap_BalanceSheetLocationAxis = aa_OtherNoncurrentLiabilitiesAndDeferredCreditsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMineAndRefineryCompanyMember | 4,000,000 us-gaap_GuaranteeObligationsCurrentCarryingValue / us-gaap_BalanceSheetLocationAxis = aa_OtherNoncurrentLiabilitiesAndDeferredCreditsMember / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMineAndRefineryCompanyMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of amount required to be contributed in the event Alcoa would be required to make payments under the guarantees |  |  |  |  |  |  |  |  |  |  |  |  |  | 40.00%aa_GuaranteeObligationPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = aa_MaadenAlcoaJointVentureMineAndRefineryCompanyMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Investment percentage |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25.49%aa_InvestmentPercentage / dei_LegalEntityAxis = aa_EstreitoProjectMember | 25.49%aa_InvestmentPercentage / dei_LegalEntityAxis = aa_EstreitoProjectMember |  |  |  |  |  |  | 20.00%aa_InvestmentPercentage / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember | 20.00%aa_InvestmentPercentage / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember |  |  |  |  |  |  |  |
Assured power from installed capacity |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 150 aa_AssuredPowerFromInstalledCapacity / dei_LegalEntityAxis = aa_EstreitoProjectMember | 150 aa_AssuredPowerFromInstalledCapacity / dei_LegalEntityAxis = aa_EstreitoProjectMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated project costs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1,590,000,000 aa_EstimatedProjectCostOfConstructionAndMaintenance / dei_LegalEntityAxis = aa_EstreitoProjectMember | 5,170,000,000 aa_EstimatedProjectCostOfConstructionAndMaintenance / dei_LegalEntityAxis = aa_EstreitoProjectMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aluminio's share of project |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 400,000,000 aa_ShareOfProject / dei_LegalEntityAxis = aa_EstreitoProjectMember | 1,320,000,000 aa_ShareOfProject / dei_LegalEntityAxis = aa_EstreitoProjectMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Commitment expended on the project |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 390,000,000 aa_ContributedAmountToProject / dei_LegalEntityAxis = aa_EstreitoProjectMember | 1,270,000,000 aa_ContributedAmountToProject / dei_LegalEntityAxis = aa_EstreitoProjectMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Prepayments made under the agreement for future gas transmission services |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 279,000,000 us-gaap_PrepaidExpenseCurrentAndNoncurrent / invest_InvestmentAxis = aa_ThreeYearEquityCallPlanMember / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember | 362,000,000 us-gaap_PrepaidExpenseCurrentAndNoncurrent / invest_InvestmentAxis = aa_ThreeYearEquityCallPlanMember / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember |  |  |  |
Range of reasonable possible loss, maximum |  |  | $ 329,000,000 us-gaap_LossContingencyRangeOfPossibleLossMaximum | € 303,000,000 us-gaap_LossContingencyRangeOfPossibleLossMaximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 400,000,000 us-gaap_LossContingencyRangeOfPossibleLossMaximum / invest_InvestmentAxis = aa_ThreeYearEquityCallPlanMember / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember | 520,000,000 us-gaap_LossContingencyRangeOfPossibleLossMaximum / invest_InvestmentAxis = aa_ThreeYearEquityCallPlanMember / us-gaap_StatementGeographicalAxis = aa_DampierGasPipelineMember |  |  |  |

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- Definition Aluminum sold in metric ton per month by facility. + References No definition available. + Details
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- Definition Environmental remediation damages. + References No definition available. + Details
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- Definition Environmental remediation payments for emergency action and natural resources damages. + References No definition available. + Details
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- Definition The number of companies in a joint venture. + References No definition available. + Details
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- Definition Percentage of payments and remediation costs under administrative agreement. + References No definition available. + Details
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- Definition Percentage of penalty on amount of additional taxes due. + References No definition available. + Details
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- Definition Period of assessment in administrative appeal. + References No definition available. + Details
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- Definition Period of environmental remediation damages. + References No definition available. + Details
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- Definition Total share of project. + References No definition available. + Details
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- Definition The Increase or Decrease in the accrual for environmental loss in the period from revisions in estimates to existing obligations. The amount does not relate to changes in the environmental accrual related to business acquisitions or divestitures, or to currency movements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q2) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 + Details
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- Definition Increase (decrease) in the accrual for environmental loss contingencies during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q2) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 + Details
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- Definition This element represents the total consolidated (as applicable) capitalization of the entity which is comprised of its long-term debt and equity instruments. The table may be detailed by subsidiary (legal entity) and include information by type of debt or equity detailed by instrument. + References No definition available. + Details
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- Definition Cost incurred in providing environmental engineering and consulting; environmental testing and analysis; and remediation services during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.2(d)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 + Details
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- Definition Amount of the required periodic payments applied to interest. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 + Details
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- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571 + Details
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- Definition This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35755396&loc=d3e33749-111570 + Details
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- Definition The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248 + Details
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- Definition A credit or adjustment for government or taxing authority authorized decrease in taxes owed as a result of meeting certain tax policy conditions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 + Details
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- Definition Estimated amount of loss resulting from an adverse tax position. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (d)(3) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
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- Definition The estimated maximum amount of possible loss from the contingency. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 9 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349 + Details
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- Definition The cash outflow associated with the purchase of or advances to an equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 13 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3213-108585 + Details
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