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Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) (USD $) | 9 Months Ended
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Sep. 30, 2012
Interrelationship Of Future Aluminum And Oil Prices [Member] | Aluminum Contracts [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Derivative Assets, Fair Value | $ 2,000,000
Interrelationship Of Future Aluminum And Oil Prices [Member] | Aluminum Contracts [Member] | Minimum [Member] | Discounted Cash Flow [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Expected future aluminum prices | 2,084
Maturity year of future aluminum price | 2012
Expected future oil prices | 91
Interrelationship Of Future Aluminum And Oil Prices [Member] | Aluminum Contracts [Member] | Maximum [Member] | Discounted Cash Flow [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Expected future aluminum prices | 2,600
Maturity year of future aluminum price | 2018
Expected future oil prices | 112
Interrelationship Of Future Aluminum Prices, Foreign Currency Exchange Rates, And US Consumer Price Index [Member] | Aluminum Contracts [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Derivative Assets, Fair Value | 607,000,000
Interrelationship Of Future Aluminum Prices, Foreign Currency Exchange Rates, And US Consumer Price Index [Member] | Aluminum Contracts [Member] | Discounted Cash Flow [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Consumer price index base year | 1982
Consumer price index base | 100
Interrelationship Of Future Aluminum Prices, Foreign Currency Exchange Rates, And US Consumer Price Index [Member] | Aluminum Contracts [Member] | Minimum [Member] | Discounted Cash Flow [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Expected future aluminum prices | 2,090
Maturity year of future aluminum price | 2012
Foreign currency exchange rate | 1
Foreign currency exchange rate | 1.03
Foreign currency exchange rate expected year | 2012
Expected Consumer price index | 227
Expected Consumer price index, Year | 2012
Interrelationship Of Future Aluminum Prices, Foreign Currency Exchange Rates, And US Consumer Price Index [Member] | Aluminum Contracts [Member] | Maximum [Member] | Discounted Cash Flow [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Expected future aluminum prices | 2,602
Price of aluminum beyond forward curve | 2,018
Foreign currency exchange rate | 0.89
Foreign currency exchange rate expected year | 2016
Expected Consumer price index | 250
Expected Consumer price index, Year | 2016
Price Of Aluminum Beyond Forward Curve [Member] | Aluminum Contracts [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Derivative Liabilities, Fair Value | 668,000,000
Price Of Aluminum Beyond Forward Curve [Member] | Aluminum Contracts [Member] | Minimum [Member] | Discounted Cash Flow [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Price of aluminum beyond forward curve | 2,828
Maturity data of aluminum beyond forward curve | 2023
Price Of Aluminum Beyond Forward Curve [Member] | Aluminum Contracts [Member] | Maximum [Member] | Discounted Cash Flow [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Price of aluminum beyond forward curve | 3,048
Maturity data of aluminum beyond forward curve | 2027
Credit Spread Between Alcoa And Counterparty [Member] | Embedded Credit Derivative [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Derivative Liabilities, Fair Value | 35,000,000
Credit Spread Between Alcoa And Counterparty [Member] | Embedded Credit Derivative [Member] | Discounted Cash Flow [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Percentage of credit spread | 1.97%
Credit Spread Between Alcoa And Counterparty [Member] | Embedded Credit Derivative [Member] | Minimum [Member] | Discounted Cash Flow [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Percentage of credit spread | 1.45%
Credit Spread Between Alcoa And Counterparty [Member] | Embedded Credit Derivative [Member] | Maximum [Member] | Discounted Cash Flow [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Percentage of credit spread | 2.49%
Price Of Electricity Beyond Forward Curve [Member] | Energy Contracts [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Derivative Liabilities, Fair Value | 8,000,000
Price Of Electricity Beyond Forward Curve [Member] | Energy Contracts [Member] | Minimum [Member] | Discounted Cash Flow [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Price of electricity beyond forward curve | 77
Maturity date of electricity beyond forward curve | 2012
Price Of Electricity Beyond Forward Curve [Member] | Energy Contracts [Member] | Maximum [Member] | Discounted Cash Flow [Member] |
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items] |
Price of electricity beyond forward curve | $ 170
Maturity date of electricity beyond forward curve | 2036

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