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Derivatives and Other Financial Instruments - Schedule of Quantitative Information for Level 3 Derivative Contracts (Detail) (USD $)
 6 Months Ended 6 Months Ended 6 Months Ended 6 Months Ended 6 Months Ended 6 Months Ended
Jun. 30, 2013
Dec. 31, 2012
Jun. 30, 2013
Aluminum Contracts [Member]
Dec. 31, 2012
Aluminum Contracts [Member]
Jun. 30, 2013
Interrelationship of Future Aluminum and Oil Prices [Member]
Aluminum Contracts [Member]
Jun. 30, 2013
Interrelationship of Future Aluminum and Oil Prices [Member]
Aluminum Contracts [Member]
Minimum [Member]
Discounted Cash Flow [Member]
Jun. 30, 2013
Interrelationship of Future Aluminum and Oil Prices [Member]
Aluminum Contracts [Member]
Maximum [Member]
Discounted Cash Flow [Member]
Jun. 30, 2013
Interrelationship of Future Aluminum Prices, Foreign Currency Exchange Rates, and U.S. Consumer Price Index [Member]
Aluminum Contracts [Member]
Jun. 30, 2013
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
Jun. 30, 2013
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
Jun. 30, 2013
Interrelationship of LME Price to Overall Energy Price [Member]
Aluminum Contracts [Member]
Jun. 30, 2013
Interrelationship of LME Price to Overall Energy Price [Member]
Aluminum Contracts [Member]
Minimum [Member]
Discounted Cash Flow [Member]
Jun. 30, 2013
Interrelationship of LME Price to Overall Energy Price [Member]
Aluminum Contracts [Member]
Maximum [Member]
Discounted Cash Flow [Member]
Jun. 30, 2013
Price of Electricity Beyond Forward Curve [Member]
Energy Contracts [Member]
Jun. 30, 2013
Price of Electricity Beyond Forward Curve [Member]
Energy Contracts [Member]
Minimum [Member]
Discounted Cash Flow [Member]
Jun. 30, 2013
Price of Electricity Beyond Forward Curve [Member]
Energy Contracts [Member]
Maximum [Member]
Discounted Cash Flow [Member]
Jun. 30, 2013
Price of Aluminum Beyond Forward Curve [Member]
Aluminum Contracts [Member]
Jun. 30, 2013
Price of Aluminum Beyond Forward Curve [Member]
Aluminum Contracts [Member]
Minimum [Member]
Discounted Cash Flow [Member]
Jun. 30, 2013
Price of Aluminum Beyond Forward Curve [Member]
Aluminum Contracts [Member]
Maximum [Member]
Discounted Cash Flow [Member]
Jun. 30, 2013
Credit Spread Between Alcoa and Counterparty [Member]
Embedded Credit Derivative [Member]
Jun. 30, 2013
Credit Spread Between Alcoa and Counterparty [Member]
Embedded Credit Derivative [Member]
Minimum [Member]
Discounted Cash Flow [Member]
Jun. 30, 2013
Credit Spread Between Alcoa and Counterparty [Member]
Embedded Credit Derivative [Member]
Maximum [Member]
Discounted Cash Flow [Member]
Jun. 30, 2013
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 $ 146,000,000 $ 117,000,000 $ 110,000,000 $ 72,000,000 $ 1,000,000     $ 411,000,000     $ 20,000,000                         
Price of aluminum beyond forward curve                                   2,485 2,673        
Derivative Liabilities, Fair value 177,000,000 86,000,000 171,000,000 69,000,000                         395,000,000     39,000,000      
Expected future aluminum prices           1,729 2,215   1,729 2,055   1,822 2,262                    
Maturity year of future aluminum price           2013 2018   2013 2016   2013 2019         2023 2027        
Expected future oil prices           88 103                                
Percentage of credit spread                                         2.05% 2.92% 2.48%
Price of electricity beyond forward curve                             $ 80 $ 154              
Maturity year of future oil price           2018 2013                                
Maturity date of electricity beyond forward curve                             2013 2036              
Foreign currency exchange rate                 1                            
Foreign currency exchange rate                 0.93 0.86                          
Foreign currency exchange rate expected year                 2013 2016                          
Consumer price index base year                   1982                          
Expected consumer price index                 231 250                          
Consumer price index base                   100                          
Expected consumer price index, Year                 2013 2016