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Noncontrolling Interests - Schedule of Noncontrolling Shareholders' Interests (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Other	$ 14us-gaap_OtherMinorityInterests	$ 33us-gaap_OtherMinorityInterests
Noncontrolling shareholders' interests	2,488us-gaap_MinorityInterest	2,929us-gaap_MinorityInterest
Alcoa World Alumina and Chemicals [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Noncontrolling shareholders' interests	$ 2,474us-gaap_MinorityInterest / dei_LegalEntityAxis = aa_AlcoaWorldAluminaAndChemicalsMember	$ 2,896us-gaap_MinorityInterest / dei_LegalEntityAxis = aa_AlcoaWorldAluminaAndChemicalsMember

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- Details

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- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which is directly or indirectly attributable to that ownership interest in subsidiary equity which is not attributable to the parent (that is, noncontrolling interest, previously referred to as minority interest).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.31)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 27

-Article 5



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 20

-Article 7

+ Details

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- Definition

Carrying amount of equity interests owned by noncontrolling shareholders, partners, or other equity holders in one or more of the entities consolidated into the reporting entity's financial statements other than joint ventures, limited partnerships, operating partnerships or interests held by preferred unit holders.

+ References

No definition available.

+ Details

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