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Derivatives and Other Financial Instruments - Schedule of Reconciliation of Activity for Derivative Contracts (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Aluminum Contracts [Member] | Assets [Member]
    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Balance at beginning of year $ 10  
Sales (8)  
Cost of goods sold (107)  
Other income, net 16  
Other comprehensive loss 10 5
Purchases, sales, issuances, and settlements 596 5
Transfers into and (or) out of Level 3      
Foreign currency translation 30  
Balance at end of year 547 10
Sales      
Cost of goods sold      
Other income, net 16  
Aluminum Contracts [Member] | Liabilities [Member]
    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Balance at beginning of year 602 702
Sales (33) (63)
Other comprehensive loss 39 (37)
Transfers into and (or) out of Level 3      
Balance at end of year 608 602
Sales      
Cost of goods sold      
Energy Contracts [Member] | Assets [Member]
    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Balance at beginning of year 2 9
Other comprehensive loss 1 (7)
Transfers into and (or) out of Level 3      
Balance at end of year 3 2
Sales      
Cost of goods sold      
Energy Contracts [Member] | Liabilities [Member]
    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Balance at beginning of year   62
Cost of goods sold   (14)
Other income, net   (48)
Transfers into and (or) out of Level 3      
Sales      
Cost of goods sold      
Embedded Credit Derivative [Member] | Liabilities [Member]
    
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]    
Balance at beginning of year 28 24
Cost of goods sold (1) (1)
Other income, net 3 5
Transfers into and (or) out of Level 3      
Balance at end of year 30 28
Sales      
Cost of goods sold      
Other income, net $ 3 $ 5