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Restructuring and Other Charges - Activity and Reserve Balances for Restructuring Charges (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 12 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014 | Dec. 31, 2014
Restructuring Cost and Reserve [Line Items] |  |  |
Other layoff cost including reclassification in pension cost | $ 19 us-gaap_OtherRestructuringCosts |  | $ 246 us-gaap_OtherRestructuringCosts
Restructuring and other charges | 177 us-gaap_RestructuringCharges | 461 us-gaap_RestructuringCharges |
Pension Costs [Member] |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Other layoff cost including reclassification in pension cost | 3 us-gaap_OtherRestructuringCosts / us-gaap_RestructuringCostAndReserveAxis = us-gaap_PensionCostsMember |  | 26 us-gaap_OtherRestructuringCosts / us-gaap_RestructuringCostAndReserveAxis = us-gaap_PensionCostsMember
Asset Retirement Obligations [Member] |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Restructuring and other charges | 95 us-gaap_RestructuringCharges / us-gaap_RestructuringCostAndReserveAxis = aa_AssetRetirementObligationsMember |  |
Environmental Remediation [Member] |  |  |
Restructuring Cost and Reserve [Line Items] |  |  |
Restructuring and other charges | $ 47 us-gaap_RestructuringCharges / us-gaap_RestructuringCostAndReserveAxis = aa_EnvironmentalRemediationMember |  |

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- Definition Amount of other expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses associated with a discontinued operation or an asset retirement obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.P.4(b)) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.P.3) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140864-122747 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section P -Subsection 3, 4 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | debit
Period Type: | duration

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- Definition Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6394359&loc=d3e17939-110869 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 5.P.4(b)) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140904-122747 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 420 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.P.3) -URI http://asc.fasb.org/extlink&oid=27011515&loc=d3e140864-122747 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 5 -Section P -Subsection 3, 4 + Details
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- Details
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- Details
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- Details
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- Details
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