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Segment Information - Schedule of Operating Results of Alcoa's Reportable Segment (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Segment Reporting Information [Line Items] |  |
Total sales | $ 5,819 us-gaap_SalesRevenueGoodsNet | $ 5,454 us-gaap_SalesRevenueGoodsNet
Equity loss | (19)aa_SegmentReportingInformationEquityInNetIncomeOfEquityMethodInvesteesOfSegments | (38)aa_SegmentReportingInformationEquityInNetIncomeOfEquityMethodInvesteesOfSegments
Depreciation, depletion, and amortization | 305 aa_SegmentReportingInformationDepreciationDepletionAndAmortizationExpenses | 319 aa_SegmentReportingInformationDepreciationDepletionAndAmortizationExpenses
Income taxes | 264 aa_SegmentReportingInformationIncomeTaxExpensesBenefits | 154 aa_SegmentReportingInformationIncomeTaxExpensesBenefits
After-tax operating income (ATOI) | 633 aa_SegmentReportingInformationProfitsLosses | 325 aa_SegmentReportingInformationProfitsLosses
Operating Segments [Member] |  |
Segment Reporting Information [Line Items] |  |
Total sales | 6,998 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember | 6,676 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember
Intersegment Eliminations [Member] |  |
Segment Reporting Information [Line Items] |  |
Intersegment sales | 1,229 aa_SegmentReportingInformationIntersegmentRevenues / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember | 1,287 aa_SegmentReportingInformationIntersegmentRevenues / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember
Third-Party Sales [Member] | Operating Segments [Member] |  |
Segment Reporting Information [Line Items] |  |
Third-party sales | 5,769 aa_SegmentReportingInformationRevenuesFromExternalCustomers / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = aa_ThirdPartySalesMember | 5,389 aa_SegmentReportingInformationRevenuesFromExternalCustomers / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = aa_ThirdPartySalesMember
Alumina [Member] |  |
Segment Reporting Information [Line Items] |  |
Equity loss | (7)aa_SegmentReportingInformationEquityInNetIncomeOfEquityMethodInvesteesOfSegments / us-gaap_StatementBusinessSegmentsAxis = aa_AluminaMember | (5)aa_SegmentReportingInformationEquityInNetIncomeOfEquityMethodInvesteesOfSegments / us-gaap_StatementBusinessSegmentsAxis = aa_AluminaMember
Depreciation, depletion, and amortization | 80 aa_SegmentReportingInformationDepreciationDepletionAndAmortizationExpenses / us-gaap_StatementBusinessSegmentsAxis = aa_AluminaMember | 97 aa_SegmentReportingInformationDepreciationDepletionAndAmortizationExpenses / us-gaap_StatementBusinessSegmentsAxis = aa_AluminaMember
Income taxes | 92 aa_SegmentReportingInformationIncomeTaxExpensesBenefits / us-gaap_StatementBusinessSegmentsAxis = aa_AluminaMember | 40 aa_SegmentReportingInformationIncomeTaxExpensesBenefits / us-gaap_StatementBusinessSegmentsAxis = aa_AluminaMember
After-tax operating income (ATOI) | 221 aa_SegmentReportingInformationProfitsLosses / us-gaap_StatementBusinessSegmentsAxis = aa_AluminaMember | 92 aa_SegmentReportingInformationProfitsLosses / us-gaap_StatementBusinessSegmentsAxis = aa_AluminaMember
Alumina [Member] | Operating Segments [Member] |  |
Segment Reporting Information [Line Items] |  |
Total sales | 1,388 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = aa_AluminaMember | 1,355 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = aa_AluminaMember
Alumina [Member] | Intersegment Eliminations [Member] |  |
Segment Reporting Information [Line Items] |  |
Intersegment sales | 501 aa_SegmentReportingInformationIntersegmentRevenues / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember / us-gaap_StatementBusinessSegmentsAxis = aa_AluminaMember | 510 aa_SegmentReportingInformationIntersegmentRevenues / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember / us-gaap_StatementBusinessSegmentsAxis = aa_AluminaMember
Alumina [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |
Segment Reporting Information [Line Items] |  |
Third-party sales | 887 aa_SegmentReportingInformationRevenuesFromExternalCustomers / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = aa_ThirdPartySalesMember / us-gaap_StatementBusinessSegmentsAxis = aa_AluminaMember | 845 aa_SegmentReportingInformationRevenuesFromExternalCustomers / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = aa_ThirdPartySalesMember / us-gaap_StatementBusinessSegmentsAxis = aa_AluminaMember
Primary Metals [Member] |  |
Segment Reporting Information [Line Items] |  |
Equity loss | (3)aa_SegmentReportingInformationEquityInNetIncomeOfEquityMethodInvesteesOfSegments / us-gaap_StatementBusinessSegmentsAxis = aa_PrimaryMetalsMember | (28)aa_SegmentReportingInformationEquityInNetIncomeOfEquityMethodInvesteesOfSegments / us-gaap_StatementBusinessSegmentsAxis = aa_PrimaryMetalsMember
Depreciation, depletion, and amortization | 109 aa_SegmentReportingInformationDepreciationDepletionAndAmortizationExpenses / us-gaap_StatementBusinessSegmentsAxis = aa_PrimaryMetalsMember | 124 aa_SegmentReportingInformationDepreciationDepletionAndAmortizationExpenses / us-gaap_StatementBusinessSegmentsAxis = aa_PrimaryMetalsMember
Income taxes | 57 aa_SegmentReportingInformationIncomeTaxExpensesBenefits / us-gaap_StatementBusinessSegmentsAxis = aa_PrimaryMetalsMember | (11)aa_SegmentReportingInformationIncomeTaxExpensesBenefits / us-gaap_StatementBusinessSegmentsAxis = aa_PrimaryMetalsMember
After-tax operating income (ATOI) | 187 aa_SegmentReportingInformationProfitsLosses / us-gaap_StatementBusinessSegmentsAxis = aa_PrimaryMetalsMember | (15)aa_SegmentReportingInformationProfitsLosses / us-gaap_StatementBusinessSegmentsAxis = aa_PrimaryMetalsMember
Primary Metals [Member] | Operating Segments [Member] |  |
Segment Reporting Information [Line Items] |  |
Total sales | 2,264 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = aa_PrimaryMetalsMember | 2,158 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = aa_PrimaryMetalsMember
Primary Metals [Member] | Intersegment Eliminations [Member] |  |
Segment Reporting Information [Line Items] |  |
Intersegment sales | 692 aa_SegmentReportingInformationIntersegmentRevenues / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember / us-gaap_StatementBusinessSegmentsAxis = aa_PrimaryMetalsMember | 734 aa_SegmentReportingInformationIntersegmentRevenues / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember / us-gaap_StatementBusinessSegmentsAxis = aa_PrimaryMetalsMember
Primary Metals [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |
Segment Reporting Information [Line Items] |  |
Third-party sales | 1,572 aa_SegmentReportingInformationRevenuesFromExternalCustomers / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = aa_ThirdPartySalesMember / us-gaap_StatementBusinessSegmentsAxis = aa_PrimaryMetalsMember | 1,424 aa_SegmentReportingInformationRevenuesFromExternalCustomers / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = aa_ThirdPartySalesMember / us-gaap_StatementBusinessSegmentsAxis = aa_PrimaryMetalsMember
Global Rolled Products [Member] |  |
Segment Reporting Information [Line Items] |  |
Equity loss | (9)aa_SegmentReportingInformationEquityInNetIncomeOfEquityMethodInvesteesOfSegments / us-gaap_StatementBusinessSegmentsAxis = aa_GlobalRolledProductsMember | (5)aa_SegmentReportingInformationEquityInNetIncomeOfEquityMethodInvesteesOfSegments / us-gaap_StatementBusinessSegmentsAxis = aa_GlobalRolledProductsMember
Depreciation, depletion, and amortization | 56 aa_SegmentReportingInformationDepreciationDepletionAndAmortizationExpenses / us-gaap_StatementBusinessSegmentsAxis = aa_GlobalRolledProductsMember | 58 aa_SegmentReportingInformationDepreciationDepletionAndAmortizationExpenses / us-gaap_StatementBusinessSegmentsAxis = aa_GlobalRolledProductsMember
Income taxes | 26 aa_SegmentReportingInformationIncomeTaxExpensesBenefits / us-gaap_StatementBusinessSegmentsAxis = aa_GlobalRolledProductsMember | 34 aa_SegmentReportingInformationIncomeTaxExpensesBenefits / us-gaap_StatementBusinessSegmentsAxis = aa_GlobalRolledProductsMember
After-tax operating income (ATOI) | 34 aa_SegmentReportingInformationProfitsLosses / us-gaap_StatementBusinessSegmentsAxis = aa_GlobalRolledProductsMember | 59 aa_SegmentReportingInformationProfitsLosses / us-gaap_StatementBusinessSegmentsAxis = aa_GlobalRolledProductsMember
Global Rolled Products [Member] | Operating Segments [Member] |  |
Segment Reporting Information [Line Items] |  |
Total sales | 1,657 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = aa_GlobalRolledProductsMember | 1,720 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = aa_GlobalRolledProductsMember
Global Rolled Products [Member] | Intersegment Eliminations [Member] |  |
Segment Reporting Information [Line Items] |  |
Intersegment sales | 36 aa_SegmentReportingInformationIntersegmentRevenues / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember / us-gaap_StatementBusinessSegmentsAxis = aa_GlobalRolledProductsMember | 43 aa_SegmentReportingInformationIntersegmentRevenues / us-gaap_ConsolidationItemsAxis = us-gaap_IntersegmentEliminationMember / us-gaap_StatementBusinessSegmentsAxis = aa_GlobalRolledProductsMember
Global Rolled Products [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |
Segment Reporting Information [Line Items] |  |
Third-party sales | 1,621 aa_SegmentReportingInformationRevenuesFromExternalCustomers / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = aa_ThirdPartySalesMember / us-gaap_StatementBusinessSegmentsAxis = aa_GlobalRolledProductsMember | 1,677 aa_SegmentReportingInformationRevenuesFromExternalCustomers / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = aa_ThirdPartySalesMember / us-gaap_StatementBusinessSegmentsAxis = aa_GlobalRolledProductsMember
Engineered Products and Solutions [Member] |  |
Segment Reporting Information [Line Items] |  |
Depreciation, depletion, and amortization | 60 aa_SegmentReportingInformationDepreciationDepletionAndAmortizationExpenses / us-gaap_StatementBusinessSegmentsAxis = aa_EngineeredProductsAndSolutionsMember | 40 aa_SegmentReportingInformationDepreciationDepletionAndAmortizationExpenses / us-gaap_StatementBusinessSegmentsAxis = aa_EngineeredProductsAndSolutionsMember
Income taxes | 89 aa_SegmentReportingInformationIncomeTaxExpensesBenefits / us-gaap_StatementBusinessSegmentsAxis = aa_EngineeredProductsAndSolutionsMember | 91 aa_SegmentReportingInformationIncomeTaxExpensesBenefits / us-gaap_StatementBusinessSegmentsAxis = aa_EngineeredProductsAndSolutionsMember
After-tax operating income (ATOI) | 191 aa_SegmentReportingInformationProfitsLosses / us-gaap_StatementBusinessSegmentsAxis = aa_EngineeredProductsAndSolutionsMember | 189 aa_SegmentReportingInformationProfitsLosses / us-gaap_StatementBusinessSegmentsAxis = aa_EngineeredProductsAndSolutionsMember
Engineered Products and Solutions [Member] | Operating Segments [Member] |  |
Segment Reporting Information [Line Items] |  |
Total sales | 1,689 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = aa_EngineeredProductsAndSolutionsMember | 1,443 us-gaap_SalesRevenueGoodsNet / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_StatementBusinessSegmentsAxis = aa_EngineeredProductsAndSolutionsMember
Engineered Products and Solutions [Member] | Third-Party Sales [Member] | Operating Segments [Member] |  |
Segment Reporting Information [Line Items] |  |
Third-party sales | $ 1,689 aa_SegmentReportingInformationRevenuesFromExternalCustomers / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = aa_ThirdPartySalesMember / us-gaap_StatementBusinessSegmentsAxis = aa_EngineeredProductsAndSolutionsMember | $ 1,443 aa_SegmentReportingInformationRevenuesFromExternalCustomers / us-gaap_ConsolidationItemsAxis = us-gaap_OperatingSegmentsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = aa_ThirdPartySalesMember / us-gaap_StatementBusinessSegmentsAxis = aa_EngineeredProductsAndSolutionsMember

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