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Derivatives and Other Financial Instruments - Schedule of Reconciliation of Activity for Derivative Contracts (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Mar. 31, 2013
Aluminum contracts [Member] | Assets [Member]
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Beginning balance $ 547
Sales (2)
Cost of goods sold (52)
Other income, net 17
Other comprehensive income 7
Purchases, sales, issuances, and settlements   
Transfers into and (or) out of Level 3   
Foreign currency translation 5
Ending balance 522
Sales   
Cost of goods sold   
Other income, net 17
Aluminum contracts [Member] | Liabilities [Member]
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Beginning balance 608
Sales (8)
Cost of goods sold   
Other income, net   
Other comprehensive income (122)
Purchases, sales, issuances, and settlements   
Transfers into and (or) out of Level 3   
Foreign currency translation   
Ending balance 478
Sales   
Cost of goods sold   
Other income, net   
Energy contracts [Member] | Assets [Member]
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Beginning balance 3
Sales   
Cost of goods sold   
Other income, net   
Other comprehensive income 5
Purchases, sales, issuances, and settlements   
Transfers into and (or) out of Level 3   
Foreign currency translation   
Ending balance 8
Sales   
Cost of goods sold   
Other income, net   
Embedded credit derivative [Member] | Liabilities [Member]
  
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]  
Beginning balance 30
Sales   
Cost of goods sold   
Other income, net 2
Other comprehensive income   
Purchases, sales, issuances, and settlements   
Transfers into and (or) out of Level 3   
Foreign currency translation   
Ending balance 32
Sales   
Cost of goods sold   
Other income, net $ 2