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Schedule Of Carrying Values And Fair Values Of Other Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Cash and Cash Equivalents
Derivative [Line Items]
Carrying value	$ 1,712	$ 1,939
Fair value	1,712	1,939
Restricted Cash
Derivative [Line Items]
Carrying value	20	25
Fair value	20	25
Noncurrent Receivables
Derivative [Line Items]
Carrying value	21	30
Fair value	21	30
Available-for-sale Securities
Derivative [Line Items]
Carrying value	86	92
Fair value	86	92
Short-term Debt
Derivative [Line Items]
Carrying value	559	62
Fair value	559	62
Commercial Paper
Derivative [Line Items]
Carrying value	318	224
Fair value	318	224
Long Term Debt Due Within One Year
Derivative [Line Items]
Carrying value	118	445
Fair value	118	445
Long-Term Debt, Less Amount Due Within One Year
Derivative [Line Items]
Carrying value	8,547	8,640
Fair value	$ 9,274	$ 9,274

X

- Definition

Financial Instruments Owned At Carrying Value

+ References

No definition available.

+ Details

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

X

- Details

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

X

- Definition

The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 320

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6475986&loc=d3e42546-110969



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

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Paragraph 38, 40

-IssueDate 2006-05-01

-Chapter 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.



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

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-BRD

-Paragraph 80

-Subparagraph Exhibit 4-3

-IssueDate 2006-05-01

-Chapter 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant