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Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) (USD $) |  |  |  | 9 Months Ended |  | 9 Months Ended |  | 9 Months Ended |  | 9 Months Ended |  | 9 Months Ended |  | 9 Months Ended
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Sep. 30, 2014 | Dec. 31, 2013 | Sep. 30, 2012 | Sep. 30, 2014 Interrelationship of Future Aluminum and Oil Prices [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member] | Sep. 30, 2014 Interrelationship of Future Aluminum and Oil Prices [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member] | Sep. 30, 2014 Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] Aluminum Contracts [Member] | Sep. 30, 2014 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 | Sep. 30, 2014 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 | Sep. 30, 2014 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member] | Sep. 30, 2014 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member] | Sep. 30, 2014 Interrelationship of LME Price to Overall Energy Price [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member] | Sep. 30, 2014 Price of Electricity beyond Forward Curve [Member] Energy Contracts [Member] | Sep. 30, 2014 Price of Electricity beyond Forward Curve [Member] Energy Contracts [Member] Minimum [Member] Discounted Cash Flow [Member] | Sep. 30, 2014 Price of Electricity beyond Forward Curve [Member] Energy Contracts [Member] Maximum [Member] Discounted Cash Flow [Member] | Sep. 30, 2014 Price of Aluminum beyond Forward Curve [Member] Aluminum Contracts [Member] | Sep. 30, 2014 Price of Aluminum beyond Forward Curve [Member] Aluminum Contracts [Member] Minimum [Member] Discounted Cash Flow [Member] | Sep. 30, 2014 Price of Aluminum beyond Forward Curve [Member] Aluminum Contracts [Member] Maximum [Member] Discounted Cash Flow [Member] | Sep. 30, 2014 Credit Spread between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member] | Sep. 30, 2014 Credit Spread between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member] Minimum [Member] Discounted Cash Flow [Member] | Sep. 30, 2014 Credit Spread between Alcoa and Counterparty [Member] Embedded Credit Derivative [Member] Maximum [Member] Discounted Cash Flow [Member] | Sep. 30, 2014 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 | $ 249,000,000 | $ 390,000,000 | $ 596,000,000 |  |  | $ 204,000,000 |  |  | $ 13,000,000 |  |  |  |  |  |  |  |  |  |  |  |
Price of aluminum beyond forward curve |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,460 | 2,588 |  |  |  |
Derivative Liabilities, Fair value | 446,000,000 | 479,000,000 |  |  |  |  |  |  |  |  |  | 6,000,000 |  |  | 407,000,000 |  |  | 24,000,000 |  |  |
Expected future aluminum prices |  |  |  | 1,921 | 2,137 |  | 1,936 | 2,051 |  | 1,914 | 2,177 |  |  |  |  |  |  |  |  |  |
Maturity year of future aluminum price |  |  |  | 2014 | 2018 |  | 2014 | 2016 |  | 2014 | 2019 |  |  |  |  | 2025 | 2027 |  |  |  |
Expected future oil prices |  |  |  | 96 | 97 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Percentage of credit spread |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1.79% | 2.49% | 2.14%
Maturity year of future oil price |  |  |  | 2018 | 2014 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Price of electricity beyond forward curve |  |  |  |  |  |  |  |  |  |  |  |  | $ 51 | $ 100 |  |  |  |  |  |  |
Foreign currency exchange rate |  |  |  |  |  |  | 1 |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maturity date of electricity beyond forward curve |  |  |  |  |  |  |  |  |  |  |  |  | 2014 | 2036 |  |  |  |  |  |  |
Foreign currency exchange rate |  |  |  |  |  |  | 0.87 | 0.89 |  |  |  |  |  |  |  |  |  |  |  |  |
Foreign currency exchange rate expected year |  |  |  |  |  |  | 2014 | 2016 |  |  |  |  |  |  |  |  |  |  |  |  |
Consumer price index base year |  |  |  |  |  |  |  | 1982 |  |  |  |  |  |  |  |  |  |  |  |  |
Expected consumer price index |  |  |  |  |  |  | 236 | 246 |  |  |  |  |  |  |  |  |  |  |  |  |
Consumer price index base |  |  |  |  |  |  |  | 100 |  |  |  |  |  |  |  |  |  |  |  |  |
Expected consumer price index, Year |  |  |  |  |  |  | 2014 | 2016 |  |  |  |  |  |  |  |  |  |  |  |  |

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