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Income Taxes - Additional Information (Detail) - USD ($) | 3 Months Ended | 6 Months Ended | 9 Months Ended
--- | --- | --- | ---
Sep. 30, 2015 | Mar. 31, 2015 | Sep. 30, 2014 | Jun. 30, 2015 | Sep. 30, 2015 | Sep. 30, 2014
Income Tax Contingency [Line Items] |  |  |  |  |  |
Effective tax rate | 48.50% |  | 60.30% |  | 41.40% | 76.00%
U.S federal statutory rate |  |  | 35.00% |  |  | 35.00%
Income tax benefit recognized | $ 100,000,000 |  | $ 199,000,000 |  | $ 401,000,000 | $ 200,000,000
Discrete income tax charge |  |  |  |  |  | 56,000,000
Operational losses in certain foreign jurisdictions |  |  | 8,000,000 |  |  | 44,000,000
Discrete income tax benefit |  |  | 9,000,000 |  |  |
Alcoa World Alumina and Chemicals [Member] |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Discrete income tax charge |  | $ 83,000,000 |  | $ 85,000,000 |  |
Alcoa World Alumina and Chemicals [Member] | Alumina Limited [Member] |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Percent of investment in AWAC joint venture by Alumina Limited |  | 40.00% |  |  |  |
Suriname [Member] |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
U.S federal statutory rate | 35.00% |  |  |  |  |
Income tax benefit recognized | $ 0 |  |  |  |  |
Net discrete income tax charge |  |  |  |  | $ 34,000,000 |
Brazil [Member] |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Discrete income tax charge |  |  | 56,000,000 |  |  |
Italy [Member] |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Income tax benefit recognized |  |  | $ 0 |  |  |
Russia [Member] |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
U.S federal statutory rate |  |  |  |  | 35.00% |
Alcoa [Member] | Alcoa World Alumina and Chemicals [Member] |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Percent of investment in AWAC joint venture by Aloca |  | 60.00% |  |  |  |
Deferred tax liability |  | $ 50,000,000 |  | $ 51,000,000 |  |
Deferred tax asset written off as valuation allowance |  | 60.00% |  |  |  |
Foreign Jurisdictions [Member] |  |  |  |  |  |
Income Tax Contingency [Line Items] |  |  |  |  |  |
Income tax benefit recognized |  |  |  |  |  | $ 0

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