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Income Taxes - Reconciliation of U.S. Federal Statutory Rate to Alcoa's Effective Tax Rate (Parenthetical) (Detail)	12 Months Ended
	Nov. 30, 2014
Reconciliation Of Effective Income Tax Rate [Line Items]
Corporate tax rate	30.00%aa_CorporateIncomeTaxRate
Tax Year Two Thousand And Fifteen [Member]
Reconciliation Of Effective Income Tax Rate [Line Items]
Corporate tax rate	28.00%aa_CorporateIncomeTaxRate / us-gaap_TaxPeriodAxis = aa_TaxYearTwoThousandAndFifteenMember
Tax Year Two Thousand And Sixteen [Member]
Reconciliation Of Effective Income Tax Rate [Line Items]
Corporate tax rate	25.00%aa_CorporateIncomeTaxRate / us-gaap_TaxPeriodAxis = aa_TaxYearTwoThousandAndSixteenMember

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- Definition

Corporate income tax rate.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

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- Details

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X

- Details

Name:	us-gaap_TaxPeriodAxis=aa_TaxYearTwoThousandAndFifteenMember
Namespace Prefix:
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Balance Type:
Period Type:

X

- Details

Name:	us-gaap_TaxPeriodAxis=aa_TaxYearTwoThousandAndSixteenMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: