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Derivatives And Other Financial Instruments - Additional Information (Detail)
In Millions, unless otherwise specified
 6 Months Ended 6 Months Ended
Jun. 30, 2012
USD ($)
Year
MetricTon
Dec. 31, 2009
USD ($)
Dec. 31, 2009
CAD
Jun. 30, 2012
Six Year Natural Gas Supply Contract
USD ($)
Jun. 30, 2012
Level 3
USD ($)
Jun. 30, 2012
Level 1
USD ($)
Dec. 31, 2011
Level 1
USD ($)
Jun. 30, 2012
Level 2
USD ($)
Dec. 31, 2011
Level 2
USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]                  
Net unrealized loss on derivative contracts       $ 5 $ 569        
Other derivative contracts estimated term of quoted market prices, in years                   
Supply contract duration       6 years          
Amount of aluminum kmt designated as fair value hedges 462                
Face amount of debt the hedges effectively convert from fixed to floating through 2018 200                
Contracts expiration date September 2011                
Forward contract to purchase to mitigate the foreign currency risk related to a Canadian-denominated loan due in 2014   57 58            
Long-term debt, fair value           $ 8,679 $ 8,576 $ 595 $ 698