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Goodwill and Other Intangible Assets - Other Intangible Assets (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Total amortizable intangible assets, Gross carrying amount	$ 1,599us-gaap_FiniteLivedIntangibleAssetsGross	$ 1,221us-gaap_FiniteLivedIntangibleAssetsGross
Total amortizable intangible assets, Accumulated amortization	(908)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization	(868)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
Indefinite-lived trade names and trademarks	46us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill	46us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill
Total other intangible assets, Gross carrying amount	1,645us-gaap_IntangibleAssetsNetExcludingGoodwill	1,267us-gaap_IntangibleAssetsNetExcludingGoodwill
Total other intangible assets, Accumulated amortization	(908)us-gaap_FiniteLivedIntangibleAssetsNet	(868)us-gaap_FiniteLivedIntangibleAssetsNet
Software [Member]
Finite-Lived Intangible Assets [Line Items]
Total amortizable intangible assets, Gross carrying amount	973us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_ComputerSoftwareIntangibleAssetMember	988us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_ComputerSoftwareIntangibleAssetMember
Total amortizable intangible assets, Accumulated amortization	(775)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_ComputerSoftwareIntangibleAssetMember	(743)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_ComputerSoftwareIntangibleAssetMember
Patent and Licenses [Member]
Finite-Lived Intangible Assets [Line Items]
Total amortizable intangible assets, Gross carrying amount	133us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = aa_PatentLicenseAgreementMember	133us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = aa_PatentLicenseAgreementMember
Total amortizable intangible assets, Accumulated amortization	(98)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = aa_PatentLicenseAgreementMember	(93)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = aa_PatentLicenseAgreementMember
Other Intangible Assets [Member]
Finite-Lived Intangible Assets [Line Items]
Total amortizable intangible assets, Gross carrying amount	493us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember	100us-gaap_FiniteLivedIntangibleAssetsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember
Total amortizable intangible assets, Accumulated amortization	$ (35)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember	$ (32)us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_OtherIntangibleAssetsMember

X

- Definition

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

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- Definition

Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

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-Publisher FASB

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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-Topic 350

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Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit.

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-Publisher FASB

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- Definition

Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges.

+ References

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-Publisher FASB

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-Topic 350

-SubTopic 30

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