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Preferred and Common Stock - Schedule of Unrecognized Compensation Expense (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012
Compensating Balances [Line Items] |
2013 | $ 38
2014 | 18
2015 | 1
Totals | $ 57

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- Definition Share Based Compensation, Unrecognized Compensation Expense Expected To Be Recognized In Year One + References No definition available. + Details
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Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Share Based Compensation, Unrecognized Compensation Expense Expected To Be Recognized In Year Three + References No definition available. + Details
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Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Share Based Compensation, Unrecognized Compensation Expense Expected To Be Recognized In Year Two + References No definition available. + Details
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Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Share Based Compensation, Unrecognized Compensation Expense Expected To Be Recognized Total + References No definition available. + Details
Name: | aa_ShareBasedCompensationUnrecognizedCompensationExpenseExpectedToBeRecognizedTotal
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_CompensatingBalancesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration