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Debt - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended	6 Months Ended		3 Months Ended		3 Months Ended		3 Months Ended			1 Months Ended	3 Months Ended	6 Months Ended
	Jun. 01, 2012	Jun. 30, 2012	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012 First Loan Agreement	Feb. 29, 2012 First Loan Agreement	Jun. 30, 2012 Two Term Loan Agreements	Jan. 31, 2012 Two Term Loan Agreements	Jun. 30, 2012 Revolving Credit Agreement Year	Feb. 29, 2012 Revolving Credit Agreement	Jan. 31, 2012 Revolving Credit Agreement	Jan. 31, 2012 Aluminio Day	Jun. 30, 2012 Aluminio Day	Jun. 30, 2012 Aluminio Day
Debt Instrument [Line Items]
Repayment of outstanding debt	$ 322		$ 659	$ 1,095									$ 215	$ 275
Outstanding debt, interest rate	6.00%
Line Of Credit Facility Amount Outstanding					150	100		350		100	100	280
Pension Contributions		$ 139	$ 352	$ 103
Applicable Margin On LIBOR					1.25%		1.50%
Line of credit facility, expiration date							Jul. 30, 2012		Dec. 31, 2012
Revolving credit facility, term									5
Weighted-average interest rate													2.32%
Weighted-average maturity days

X

- Definition

Applicable margin on London Inter Bank Offer Rate loans.

+ References

No definition available.

+ Details

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X

- Definition

Debt weighted average maturity days.

+ References

No definition available.

+ Details

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X

- Definition

Line Of Credit Facility, Term

+ References

No definition available.

+ Details

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Data Type:	xbrli:decimalItemType
Balance Type:	na
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X

- Definition

Weighted Average Interest Rate, Outstanding Borrowings

+ References

No definition available.

+ Details

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Namespace Prefix:	aa_
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Balance Type:	na
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X

- Definition

Interest rate stated in the contractual debt agreement.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

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

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- Details

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X

- Definition

Amount borrowed under the credit facility as of the balance sheet date.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

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Namespace Prefix:	us-gaap_
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X

- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ 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 210.5-02.19(b),22(b))

-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 19, 22

-Article 5

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X

- Definition

The amount of cash or cash equivalents contributed by the entity to fund its pension plans.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 28

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3536-108585

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X

- Definition

The cash outflow for debt initially having maturity due after one year or beyond the normal operating cycle, if longer.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 18

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3291-108585



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 20

-Subparagraph b

-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.

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