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Segment Information - Schedule of Segment ATOI to Consolidated Net Income (Loss) Attributable to Alcoa (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended
--- | ---
Mar. 31, 2015 | Mar. 31, 2014
Segment Reporting Information [Line Items] |  |
Total segment ATOI | $ 633 aa_SegmentReportingInformationProfitsLosses | $ 325 aa_SegmentReportingInformationProfitsLosses
Interest expense | (122)us-gaap_InterestExpense | (120)us-gaap_InterestExpense
Noncontrolling interests | (60)us-gaap_NetIncomeLossAttributableToNoncontrollingInterest | 19 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest
Net income (loss) attributable to Alcoa | 195 us-gaap_NetIncomeLoss | (178)us-gaap_NetIncomeLoss
Other [Member] |  |
Segment Reporting Information [Line Items] |  |
Impact of LIFO | 7 aa_SegmentReportingInformationImpactOfLastInFirstOut / us-gaap_ConsolidationItemsAxis = us-gaap_MaterialReconcilingItemsMember | (7)aa_SegmentReportingInformationImpactOfLastInFirstOut / us-gaap_ConsolidationItemsAxis = us-gaap_MaterialReconcilingItemsMember
Interest expense | (80)us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_MaterialReconcilingItemsMember | (78)us-gaap_InterestExpense / us-gaap_ConsolidationItemsAxis = us-gaap_MaterialReconcilingItemsMember
Noncontrolling interests | (60)us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / us-gaap_ConsolidationItemsAxis = us-gaap_MaterialReconcilingItemsMember | 19 us-gaap_NetIncomeLossAttributableToNoncontrollingInterest / us-gaap_ConsolidationItemsAxis = us-gaap_MaterialReconcilingItemsMember
Corporate expense | (64)aa_SegmentReportingInformationCorporateExpenses / us-gaap_ConsolidationItemsAxis = us-gaap_MaterialReconcilingItemsMember | (67)aa_SegmentReportingInformationCorporateExpenses / us-gaap_ConsolidationItemsAxis = us-gaap_MaterialReconcilingItemsMember
Restructuring and other charges | (161)aa_SegmentReportingInformationRestructuringAndOtherCharges / us-gaap_ConsolidationItemsAxis = us-gaap_MaterialReconcilingItemsMember | (321)aa_SegmentReportingInformationRestructuringAndOtherCharges / us-gaap_ConsolidationItemsAxis = us-gaap_MaterialReconcilingItemsMember
Other | $ (80)aa_SegmentReportingInformationOtherIncomeExpenseNet / us-gaap_ConsolidationItemsAxis = us-gaap_MaterialReconcilingItemsMember | $ (49)aa_SegmentReportingInformationOtherIncomeExpenseNet / us-gaap_ConsolidationItemsAxis = us-gaap_MaterialReconcilingItemsMember

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- Definition Amount of the cost of borrowed funds accounted for as interest expense. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.9) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 9 -Article 9 + Details
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