Income Taxes - Reconciliation of U.S. Federal Statutory Rate to Alcoa's Effective Tax Rate for Continuing Operations (Detail)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Taxes [Line Items]
U.S. federal statutory rate	35.00%	35.00%	35.00%
Taxes on foreign operations	(0.10%)	(11.00%)	(5.40%)
Permanent differences on restructuring charges and asset disposals	10.80%		0.70%
Audit and other adjustments to prior years' accruals	3.50%	(1.10%)	1.20%
Noncontrolling interests	3.80%	0.80%	2.60%
Statutory tax rate and law changes	(0.40%)	0.80%	(5.10%)
Tax law change related to Medicare Part D			14.40%
Changes in valuation allowances	15.20%	2.30%	(8.70%)
Amortization of goodwill related to intercompany stock sales/reorganizations	(7.70%)	(2.80%)	(5.20%)
Change in legal structure of investment	(4.10%)
Interest income related to income tax positions	(1.30%)	(0.20%)
Company-owned life insurance/split-dollar net premiums	(3.90%)	(0.20%)	(1.80%)
Other	(0.80%)	0.40%	(0.80%)
Effective tax rate	50.00%	24.00%	26.90%

Effective Income Tax Rate Reconciliation, Non-Taxable Interest Income

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A ratio calculated by dividing the reported amount of income tax expense attributable to continuing operations for the period by GAAP-basis pretax income from continuing operations.

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The domestic federal statutory tax rate applicable under enacted tax laws to the Company's pretax income from continuing operations for the period. The "statutory" tax rate is the regular tax rate if there are alternative tax systems.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 109

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to changes in the valuation allowance for deferred tax assets.

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The portion of the difference between total income tax expense or benefit as reported in the Income Statement and the expected income tax expense or benefit that is attributable to changes in the income tax laws or rates.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 109

-Paragraph 45

-Subparagraph g

-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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Percentage of difference between the effective income tax rate and domestic federal statutory income tax rate attributable to the deduction received under enacted tax laws for Medicare prescription drug benefits (subsidies).

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by the difference between statutory income tax rates in foreign jurisdictions and the domestic federal statutory income tax rate recorded during the period.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to noncontrolling interest income or expense that is exempt from income taxes under enacted tax laws.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by the different amortization methods allowed under generally accepted accounting principles and enacted tax laws.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to nondeductible life insurance premiums under enacted tax laws.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to nondeductible restructuring charges under enacted tax laws.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to all other items not otherwise listed in the existing taxonomy.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate attributable to revisions in previously reported amounts of income tax provision.

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The portion of the difference between the effective income tax rate and domestic federal statutory income tax rate that can be explained by investment tax credits generated or utilized under enacted tax laws during the period.

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