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Properties, Plants, And Equipment, Net (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2011 MT | Dec. 31, 2010 MT
Property, Plant and Equipment [Line Items] |  |
Net carrying value of assets |  | $ 152
Smelting Assets [Member] |  |
Property, Plant and Equipment [Line Items] |  |
Net carrying value of assets | 166 | 306
Idle capacity of assets, units | 353,000 | 587,000
Net carrying value of other idled smelting assets written off | 291,000 |
Idled Refining [Member] |  |
Property, Plant and Equipment [Line Items] |  |
Net carrying value of assets | $ 65 | $ 100
Idle capacity of assets, units | 1,177,000 | 1,321,000

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- Definition Idle Capacity Of Asset + References No definition available. + Details
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Balance Type: | na
Period Type: | duration

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- Definition Net Carrying Value Of Assets + References No definition available. + Details
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Namespace Prefix: | aa_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Write Off Of The Net Carrying Value Of Other Idled Smelting Assets + References No definition available. + Details
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Namespace Prefix: | aa_
Data Type: | num:massItemType
Balance Type: | na
Period Type: | duration

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