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Derivatives and Other Financial Instruments - Gross Amounts of Recognized Derivative Assets and Liabilities and Gross Amounts Offset in Accompanying Consolidated Balance Sheet (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Margin on Derivative held from counterparties	$ 9

X

- Definition

Derivative Margin Held From Counterparty

+ References

No definition available.

+ Details

Name:	aa_DerivativeMarginHeldFromCounterparty
Namespace Prefix:	aa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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- Details

Name:	us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration