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Schedule Of Quantitative Information For Level 3 Derivative Contracts (Detail) (USD $)
 6 Months Ended
Jun. 30, 2012
Interrelationship Of Future Aluminum And Oil Prices | Aluminum Contracts
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Derivative Assets, Fair Value $ 3
Interrelationship Of Future Aluminum And Oil Prices | Aluminum Contracts | Minimum | Discounted Cash Flow
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Expected future aluminum prices 1,828
Expected future oil prices 88
Interrelationship Of Future Aluminum And Oil Prices | Aluminum Contracts | Maximum | Discounted Cash Flow
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Expected future aluminum prices 2,390
Expected future oil prices 91
Price Of Aluminum Beyond Forward Curve | Aluminum Contracts
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Derivative Liabilities, Fair Value 523
Price Of Aluminum Beyond Forward Curve | Aluminum Contracts | Minimum | Discounted Cash Flow
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Price of aluminum beyond forward curve 2,658,000,000
Maturity data of aluminum beyond forward curve 2022
Price Of Aluminum Beyond Forward Curve | Aluminum Contracts | Maximum | Discounted Cash Flow
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Price of aluminum beyond forward curve 2,896,000,000
Maturity data of aluminum beyond forward curve 2027
Credit Spread Between Alcoa And Counterparty | Embedded Credit Derivative
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Derivative Liabilities, Fair Value 39
Credit Spread Between Alcoa And Counterparty | Embedded Credit Derivative | Discounted Cash Flow
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Percentage of credit spread 2.25%
Credit Spread Between Alcoa And Counterparty | Embedded Credit Derivative | Minimum | Discounted Cash Flow
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Percentage of credit spread 2.03%
Credit Spread Between Alcoa And Counterparty | Embedded Credit Derivative | Maximum | Discounted Cash Flow
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Percentage of credit spread 2.46%
Price Of Electricity Beyond Forward Curve | Energy Contracts
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Derivative Liabilities, Fair Value 10
Price Of Electricity Beyond Forward Curve | Energy Contracts | Minimum | Discounted Cash Flow
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Price of electricity beyond forward curve 77,000,000
Maturity date of electricity beyond forward curve 2012
Price Of Electricity Beyond Forward Curve | Energy Contracts | Maximum | Discounted Cash Flow
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Price of electricity beyond forward curve $ 170,000,000
Maturity date of electricity beyond forward curve 2036