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Receivables - Additional Information (Detail) (USD $) | 0 Months Ended | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 31, 2012 | Mar. 31, 2015 Agreement | Dec. 31, 2014
Schedule Of Financial Receivables [Line Items] |  |  |
Number of arrangement with different financial institution to sell customer receivables |  | 3 aa_NumberOfArrangementsToSellCustomerReceivables |
Net cash funding received in current period |  | $ 0 aa_AmountIncludedInCommitmentOfAdditionalFundingForDevelopmentOfReserves |
Deferred purchase price receivable | 254,000,000 aa_DeferredPriceCustomerReceivables | 417,000,000 aa_DeferredPriceCustomerReceivables | 356,000,000 aa_DeferredPriceCustomerReceivables
Net cash funding received |  | 250,000,000 aa_CommitmentOfAdditionalFundingForDevelopmentOfReserves |
Amount of cash draws under arrangement |  | 1,308,000,000 aa_ProceedsFromReceivableFunding |
Amount of cash repayments under arrangement |  | 1,058,000,000 aa_RepaymentsForReceivableFunding |
Accounts receivables |  | 19,545,000,000 us-gaap_AccountsReceivableGross |
Cash collections of other receivables |  | 18,878,000,000 us-gaap_ProceedsFromCollectionOfOtherReceivables |
Minimum [Member] |  |  |
Schedule Of Financial Receivables [Line Items] |  |  |
Funding of customer receivables sold |  | 200,000,000 aa_FundingOfCustomerReceivablesSold / us-gaap_RangeAxis = us-gaap_MinimumMember |
Maximum [Member] |  |  |
Schedule Of Financial Receivables [Line Items] |  |  |
Funding of customer receivables sold |  | $ 500,000,000 aa_FundingOfCustomerReceivablesSold / us-gaap_RangeAxis = us-gaap_MaximumMember |

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- Definition Amount included in commitment of additional funding for development of reserves. + References No definition available. + Details
Name: | aa_AmountIncludedInCommitmentOfAdditionalFundingForDevelopmentOfReserves
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Commitment of additional funding for development of reserves. + References No definition available. + Details
Name: | aa_CommitmentOfAdditionalFundingForDevelopmentOfReserves
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Deferred purchase price customer receivables. + References No definition available. + Details
Name: | aa_DeferredPriceCustomerReceivables
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Funding of customer receivables sold. + References No definition available. + Details
Name: | aa_FundingOfCustomerReceivablesSold
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Number of arrangements to sell customer receivables. + References No definition available. + Details
Name: | aa_NumberOfArrangementsToSellCustomerReceivables
Namespace Prefix: | aa_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Proceeds from receivable funding. + References No definition available. + Details
Name: | aa_ProceedsFromReceivableFunding
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Repayments for receivable funding. + References No definition available. + Details
Name: | aa_RepaymentsForReceivableFunding
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Details
Name: | aa_ScheduleOfFinancialReceivablesLineItems
Namespace Prefix: | aa_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition For unclassified balance sheet, amounts due from customers or clients for goods or services that have been delivered or sold in the normal course of business. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 3 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.9) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
Name: | us-gaap_AccountsReceivableGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The cash inflow associated with the collection of other receivables not otherwise defined in the taxonomy. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3179-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Investing Activities -URI http://asc.fasb.org/extlink&oid=6516133 + Details
Name: | us-gaap_ProceedsFromCollectionOfOtherReceivables
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |