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Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2015 USD ($) Index $ / Metric_Ton $ / MWh $ / Barrels $ / AUD $ / lb | Dec. 31, 2014 USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Assets, Fair value | $ | $ 875 | $ 268
Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Assets, Fair value | $ | $ 87 |
Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 1,562 |
Maturity year of future aluminum price | 2015 |
Expected future aluminum prices | 1,562 |
Maturity year of future aluminum price | 2015 |
Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 1,615 |
Maturity year of future aluminum price | 2016 |
Expected future aluminum prices | 1,615 |
Maturity year of future aluminum price | 2016 |
Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Estimated Foreign Currency Exchange Rate [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Foreign currency exchange rate | $ / AUD | 0.70 |
Foreign currency exchange rate expected year | 2015 |
Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Estimated Foreign Currency Exchange Rate [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Foreign currency exchange rate | $ / AUD | 0.70 |
Foreign currency exchange rate expected year | 2016 |
Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Consumer Price Index [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected consumer price index | Index | 235 |
Expected consumer price index, Year | 2015 |
Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member] | Consumer Price Index [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Consumer price index base year | 1982 |
Consumer price index base | Index | 100 |
Expected consumer price index | Index | 239 |
Expected consumer price index, Year | 2016 |
Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum and Oil Prices [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 1,562 |
Maturity year of future aluminum price | 2015 |
Expected future oil prices | $ / Barrels | 47 |
Maturity year of future oil price | 2015 |
Expected future aluminum prices | 1,562 |
Maturity year of future aluminum price | 2015 |
Embedded Aluminum Derivative [Member] | Interrelationship of Future Aluminum and Oil Prices [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 1,762 |
Maturity year of future aluminum price | 2018 |
Expected future oil prices | $ / Barrels | 60 |
Maturity year of future oil price | 2018 |
Expected future aluminum prices | 1,762 |
Maturity year of future aluminum price | 2018 |
Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Assets, Fair value | $ | $ 784 |
Derivative Liabilities, Fair value | $ | $ 223 |
Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 2,160 |
Maturity year of future aluminum price | 2026 |
Expected future aluminum prices | 2,160 |
Maturity year of future aluminum price | 2026 |
Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 2,239 |
Maturity year of future aluminum price | 2027 |
Expected future aluminum prices | 2,239 |
Maturity year of future aluminum price | 2027 |
Embedded Aluminum Derivative [Member] | Interrelationship of LME Price to Overall Energy Price [Member] | Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Assets, Fair value | $ | $ 4 |
Embedded Aluminum Derivative [Member] | Interrelationship of LME Price to Overall Energy Price [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 1,560 |
Maturity year of future aluminum price | 2015 |
Expected future aluminum prices | 1,560 |
Maturity year of future aluminum price | 2015 |
Embedded Aluminum Derivative [Member] | Interrelationship of LME Price to Overall Energy Price [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 1,817 |
Maturity year of future aluminum price | 2019 |
Expected future aluminum prices | 1,817 |
Maturity year of future aluminum price | 2019 |
Embedded Aluminum Derivative [Member] | Two Contracts [Member] | Price of Aluminum beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 2,347 |
Maturity year of future aluminum price | 2029 |
Expected future aluminum prices | 2,347 |
Maturity year of future aluminum price | 2029 |
Embedded Aluminum Derivative [Member] | Two Contracts [Member] | Price of Aluminum beyond Forward Curve [Member] | Midwest Premium | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Foreign currency exchange rate expected year | 2029 |
Embedded Aluminum Derivative [Member] | One Contract [Member] | Price of Aluminum beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 2,643 |
Maturity year of future aluminum price | 2036 |
Expected future aluminum prices | 2,643 |
Maturity year of future aluminum price | 2036 |
Embedded Aluminum Derivative [Member] | One Contract [Member] | Price of Aluminum beyond Forward Curve [Member] | Midwest Premium | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Midwest Premium | $ / lb | 0.0795 |
Foreign currency exchange rate expected year | 2021 |
Embedded Aluminum Derivative [Member] | One Contract [Member] | Price of Aluminum beyond Forward Curve [Member] | Midwest Premium | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Midwest Premium | $ / lb | 0.0795 |
Foreign currency exchange rate expected year | 2036 |
Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Liabilities, Fair value | $ | $ 32 |
Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Credit Spread [Member] | Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Percentage of credit spread | 3.27% |
Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Credit Spread [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Percentage of credit spread | 3.04% |
Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Credit Spread [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Percentage of credit spread | 3.50% |
Energy Contracts [Member] | Price of Electricity beyond Forward Curve [Member] | Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Liabilities, Fair value | $ | $ 5 |
Energy Contracts [Member] | Price of Electricity beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Price of electricity beyond forward curve | $ / MWh | 45 |
Maturity date of electricity beyond forward curve | 2018 |
Energy Contracts [Member] | Price of Electricity beyond Forward Curve [Member] | Average Price [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Price of electricity beyond forward curve | $ / MWh | 121 |
Maturity date of electricity beyond forward curve | 2036 |

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