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Schedule Of Reconciliation Of Activity For Derivative Contracts (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2012
Aluminum Contracts | Assets
    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning balance $ 8 $ 10
Sales (2)  
Other expenses, net (1)  
Other comprehensive loss 5 7
Purchases, sales, issuances, and settlements*    [1]    [1]
Transfers into and (or) out of Level 3*    [1]    [1]
Ending balance 10 10
Sales   (5)
Other expenses, net   (2)
Sales   (5)
Other expenses, net   (2)
Aluminum Contracts | Liabilities
    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning balance 674 602
Sales (8)  
Other comprehensive loss (136) (54)
Purchases, sales, issuances, and settlements*    [1]    [1]
Transfers into and (or) out of Level 3*    [1]    [1]
Ending balance 530 530
Sales   (18)
Sales   (18)
Energy Contracts | Assets
    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning balance   2
Other comprehensive loss   (2)
Purchases, sales, issuances, and settlements*    [1]    [1]
Transfers into and (or) out of Level 3*    [1]    [1]
Energy Contracts | Liabilities
    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning balance 10  
Other comprehensive loss   10
Purchases, sales, issuances, and settlements*    [1]    [1]
Transfers into and (or) out of Level 3*    [1]    [1]
Ending balance 10 10
Embedded Credit Derivative | Liabilities
    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Beginning balance 28 28
Cost of goods sold 1  
Other expenses, net 10  
Purchases, sales, issuances, and settlements*    [1]    [1]
Transfers into and (or) out of Level 3*    [1]    [1]
Ending balance 39 39
Cost of goods sold   1
Other expenses, net 10 10
Cost of goods sold   1
Other expenses, net $ 10 $ 10
[1] There were no purchases, sales, issuances or settlements of Level 3 financial instruments. Additionally, there were no transfers of financial instruments into or out of Level 3.