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Contingencies and Commitments - Additional Information - 1 (Detail) (USD $) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2009
Loss Contingencies [Line Items] |  |  |
Number of cleanup locations | More than 100 |  |
Remediation reserve balance | $ 538,000,000 us-gaap_AccrualForEnvironmentalLossContingencies | $ 543,000,000 us-gaap_AccrualForEnvironmentalLossContingencies |
Remediation reserve balance, classified as a current liability | 66,000,000 us-gaap_AccruedEnvironmentalLossContingenciesCurrent | 70,000,000 us-gaap_AccruedEnvironmentalLossContingenciesCurrent |
Payments related to remediation expenses applied against the reserve | 6,000,000 us-gaap_AccrualForEnvironmentalLossContingenciesPayments |  |
Increase (Decrease) in reserves due to effects of foreign currency translation | 7,000,000 us-gaap_TranslationAdjustmentFunctionalToReportingCurrencyIncreaseDecreaseGrossOfTax |  |
Actual remediation fieldwork period | 4 years |  |
Minimum [Member] |  |  |
Loss Contingencies [Line Items] |  |  |
Planning and design phase period | 2 years |  |
Majority of the project funding period | 2016 |  |
Maximum [Member] |  |  |
Loss Contingencies [Line Items] |  |  |
Planning and design phase period | 3 years |  |
Majority of the project funding period | 2020 |  |
Recurring Costs of Managing Hazardous Substances and Environmental Programs [Member] |  |  |
Loss Contingencies [Line Items] |  |  |
Percentage of cost of goods sold | 2.00%aa_PercentageOfCostOfGoodsSold / us-gaap_LossContingenciesByNatureOfContingencyAxis = aa_RecurringCostsOfManagingHazardousSubstancesAndEnvironmentalProgramsMember |  |
Massena West, NY [Member] |  |  |
Loss Contingencies [Line Items] |  |  |
Remediation reserve balance | 238,000,000 us-gaap_AccrualForEnvironmentalLossContingencies / us-gaap_StatementGeographicalAxis = aa_MassenaNyMember | 239,000,000 us-gaap_AccrualForEnvironmentalLossContingencies / us-gaap_StatementGeographicalAxis = aa_MassenaNyMember |
Grasse River [Member] |  |  |
Loss Contingencies [Line Items] |  |  |
Increase in remediation reserve | 8,000,000 us-gaap_AccrualForEnvironmentalLossContingenciesPeriodIncreaseDecrease / us-gaap_StatementGeographicalAxis = aa_GrasseRiverMember |  |
Sherwin, TX site [Member] |  |  |
Loss Contingencies [Line Items] |  |  |
Remediation reserve balance | 32,000,000 us-gaap_AccrualForEnvironmentalLossContingencies / us-gaap_StatementGeographicalAxis = aa_SherwinTXMember | 32,000,000 us-gaap_AccrualForEnvironmentalLossContingencies / us-gaap_StatementGeographicalAxis = aa_SherwinTXMember |
Guarantees, expiration date | Through 2019 |  |
Portovesme [Member] |  |  |
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
Remediation reserve adjustment | 7,000,000 aa_EnvironmentalLossContingenciesAdjustment / us-gaap_StatementGeographicalAxis = aa_PortovesmeSiteMember |  |
Other Sites [Member] |  |  |
Loss Contingencies [Line Items] |  |  |
Remediation reserve adjustment | 1,000,000 aa_EnvironmentalLossContingenciesAdjustment / us-gaap_StatementGeographicalAxis = aa_OtherSitesMember |  |
East St. Louis, IL Site [Member] |  |  |
Loss Contingencies [Line Items] |  |  |
Remediation reserve balance | $ 15,000,000 us-gaap_AccrualForEnvironmentalLossContingencies / us-gaap_StatementGeographicalAxis = aa_EastStLouisSiteMember | $ 15,000,000 us-gaap_AccrualForEnvironmentalLossContingencies / us-gaap_StatementGeographicalAxis = aa_EastStLouisSiteMember |

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- Definition Total costs accrued as of the balance sheet date for environmental loss contingencies. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 25 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346 + Details
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- Definition Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable in twelve months or in the next operating cycle if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 20 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.20) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6911-107765 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 50 -Paragraph 10 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13237-110859 + Details
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