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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, 2016 USD ($) MWh $ / MWh $ / Metric_Ton $ / lb $ / Barrels | Dec. 31, 2015 USD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Assets, Fair value | $ | $ 317 | $ 1,137
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 | $ | 306 |
Derivative Liabilities, Fair value | $ | $ 242 |
Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 2,197 |
Maturity year of future aluminum price | 2027 |
Embedded Aluminum Derivative [Member] | Price of Aluminum beyond Forward Curve [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Expected future aluminum prices | 2,229 |
Maturity year of future aluminum price | 2027 |
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 | 2,197 |
Maturity year of future aluminum price | 2027 |
Embedded Aluminum Derivative [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 | 0.0630 |
Midwest Premium expected year | 2016 |
Embedded Aluminum Derivative [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 | 0.075 |
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 | 1,680 |
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 | 1,662 |
Maturity year of future aluminum price | 2016 |
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 | 1,802 |
Maturity year of future aluminum price | 2019 |
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] |  |
Maturity year of future aluminum price | 2016 |
Expected future oil prices | $ / Barrels | 49 |
Maturity year of future oil price | 2016 |
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 | 55 |
Maturity year of future oil price | 2018 |
Embedded Aluminum Derivative [Member] | Interrelationship of London Metal Exchange Price to Amount Of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum [Member] | Level 3 [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Derivative Liabilities, Fair value | $ | $ 30 |
Megawatt hours per year | MWh | 2,000,000 |
Embedded Aluminum Derivative [Member] | Interrelationship of London Metal Exchange Price to Amount Of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum [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 | 1,662 |
Maturity year of future aluminum price | 2016 |
Embedded Aluminum Derivative [Member] | Interrelationship of London Metal Exchange Price to Amount Of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum [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 | 1,785 |
Maturity year of future aluminum price | 2019 |
Embedded Aluminum Derivative [Member] | Interrelationship of London Metal Exchange Price to Amount Of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum [Member] | Midwest Premium | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Midwest Premium | $ / lb | 0.063 |
Midwest Premium expected year | 2016 |
Embedded Aluminum Derivative [Member] | Interrelationship of London Metal Exchange Price to Amount Of Megawatt Hours of Energy Needed to Produce Forecasted Metric Tons of Aluminum [Member] | Midwest Premium | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Midwest Premium | $ / lb | 0.075 |
Midwest Premium expected year | 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 | 2,337 |
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] |  |
Midwest Premium 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 | 2,633 |
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] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Midwest Premium expected year | 2036 |
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 Assets, Fair value | $ | $ 7 |
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 | 57 |
Maturity date of electricity beyond forward curve | 2016 |
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 | 58 |
Maturity date of electricity beyond forward curve | 2017 |
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 | $ | $ 24 |
Percentage of credit spread | 2.52% |
Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Level 3 [Member] | Minimum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Percentage of credit spread | 2.15% |
Embedded Credit Derivative [Member] | Credit Spread between Alcoa and Counterparty [Member] | Level 3 [Member] | Maximum [Member] |  |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |  |
Percentage of credit spread | 2.89% |

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