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Goodwill and Other Intangible Assets - Changes in Carrying Amount of Goodwill (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Dec. 31, 2012 Segment
Corporate [Member] |
Goodwill [Line Items] |
Segment reporting, goodwill | 1,247
Alumina [Member] |
Goodwill [Line Items] |
Segment reporting, goodwill | 161
Primary Metals [Member] |
Goodwill [Line Items] |
Segment reporting, goodwill | 751
Global Rolled Products [Member] |
Goodwill [Line Items] |
Segment reporting, goodwill | 62
Engineered Products and Solutions [Member] |
Goodwill [Line Items] |
Segment reporting, goodwill | 273
Alcoa [Member] |
Goodwill [Line Items] |
Number of reportable segments | 4

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- Definition Segment Reporting Reconciling Items Goodwill Assets. + References No definition available. + Details
Name: | aa_SegmentReportingReconcilingItemsGoodwillAssets
Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

X
- Definition Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements. + References No definition available. + Details
Name: | us-gaap_NumberOfReportableSegments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration