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Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) (USD $) |  |  |  |  |  | 6 Months Ended |  | 6 Months Ended |  | 6 Months Ended |  | 6 Months Ended |  | 6 Months Ended |  | 6 Months Ended
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Jun. 30, 2013 | Dec. 31, 2012 | Jun. 30, 2013 Aluminum Contracts [Member] | Dec. 31, 2012 Aluminum Contracts [Member] | Jun. 30, 2013 Interrelationship of Future Aluminum and Oil Prices [Member] Aluminum Contracts [Member] | Jun. 30, 2013 Interrelationship of Future Aluminum and Oil Prices [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member] | Jun. 30, 2013 Interrelationship of Future Aluminum and Oil Prices [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member] | Jun. 30, 2013 Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] Aluminum Contracts [Member] | Jun. 30, 2013 Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member] Index | Jun. 30, 2013 Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member] Index | Jun. 30, 2013 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member] | Jun. 30, 2013 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member] | Jun. 30, 2013 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member] | Jun. 30, 2013 Price of Electricity Beyond Forward Curve [Member] Energy Contracts [Member] | Jun. 30, 2013 Price of Electricity Beyond Forward Curve [Member] Energy Contracts [Member] Minimum [Member] Discounted Cash Flow [Member] | Jun. 30, 2013 Price of Electricity Beyond Forward Curve [Member] Energy Contracts [Member] Maximum [Member] Discounted Cash Flow [Member] | Jun. 30, 2013 Price of Aluminum Beyond Forward Curve [Member] Aluminum Contracts [Member] | Jun. 30, 2013 Price of Aluminum Beyond Forward Curve [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member] | Jun. 30, 2013 Price of Aluminum Beyond Forward Curve [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member] | Jun. 30, 2013 Credit Spread Between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member] | Jun. 30, 2013 Credit Spread Between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member] Minimum [Member] Discounted Cash Flow [Member] | Jun. 30, 2013 Credit Spread Between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member] Maximum [Member] Discounted Cash Flow [Member] | Jun. 30, 2013 Credit Spread Between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member] Median [Member] Discounted Cash Flow [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Derivative Assets, Fair value | $ 146,000,000 | $ 117,000,000 | $ 110,000,000 | $ 72,000,000 | $ 1,000,000 |  |  | $ 411,000,000 |  |  | $ 20,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Price of aluminum beyond forward curve |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,485 | 2,673 |  |  |  |
Derivative Liabilities, Fair value | 177,000,000 | 86,000,000 | 171,000,000 | 69,000,000 |  |  |  |  |  |  |  |  |  |  |  |  | 395,000,000 |  |  | 39,000,000 |  |  |
Expected future aluminum prices |  |  |  |  |  | 1,729 | 2,215 |  | 1,729 | 2,055 |  | 1,822 | 2,262 |  |  |  |  |  |  |  |  |  |
Maturity year of future aluminum price |  |  |  |  |  | 2013 | 2018 |  | 2013 | 2016 |  | 2013 | 2019 |  |  |  |  | 2023 | 2027 |  |  |  |
Expected future oil prices |  |  |  |  |  | 88 | 103 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of credit spread |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.05% | 2.92% | 2.48%
Price of electricity beyond forward curve |  |  |  |  |  |  |  |  |  |  |  |  |  |  | $ 80 | $ 154 |  |  |  |  |  |  |
Maturity year of future oil price |  |  |  |  |  | 2018 | 2013 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity date of electricity beyond forward curve |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2013 | 2036 |  |  |  |  |  |  |
Foreign currency exchange rate |  |  |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Foreign currency exchange rate |  |  |  |  |  |  |  |  | 0.93 | 0.86 |  |  |  |  |  |  |  |  |  |  |  |  |
Foreign currency exchange rate expected year |  |  |  |  |  |  |  |  | 2013 | 2016 |  |  |  |  |  |  |  |  |  |  |  |  |
Consumer price index base year |  |  |  |  |  |  |  |  |  | 1982 |  |  |  |  |  |  |  |  |  |  |  |  |
Expected consumer price index |  |  |  |  |  |  |  |  | 231 | 250 |  |  |  |  |  |  |  |  |  |  |  |  |
Consumer price index base |  |  |  |  |  |  |  |  |  | 100 |  |  |  |  |  |  |  |  |  |  |  |  |
Expected consumer price index, Year |  |  |  |  |  |  |  |  | 2013 | 2016 |  |  |  |  |  |  |  |  |  |  |  |  |

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