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Derivatives and Other Financial Instruments - Schedule of Fair Values and Corresponding Level of Fair Value Hierarchy of Outstanding Derivative Contracts Recorded as Assets (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2013
Dec. 31, 2012
Sep. 30, 2012
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives $ 422 $ 596 $ 596
Level 1 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 8 27  
Level 3 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 385 550  
Level 2 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 36 45  
Derivatives Designated as Hedging Instruments [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 56 81  
Derivatives Designated as Hedging Instruments [Member] | Prepaid Expenses and Other Current Assets [Member] | Aluminum Contracts [Member] | Level 1 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 3 23  
Derivatives Designated as Hedging Instruments [Member] | Prepaid Expenses and Other Current Assets [Member] | Aluminum Contracts [Member] | Level 3 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 8 7  
Derivatives Designated as Hedging Instruments [Member] | Prepaid Expenses and Other Current Assets [Member] | Foreign Exchange Contracts [Member] | Level 1 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 5    
Derivatives Designated as Hedging Instruments [Member] | Prepaid Expenses and Other Current Assets [Member] | Interest Rate Contracts [Member] | Level 2 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 6 8  
Derivatives Designated as Hedging Instruments [Member] | Other Noncurrent Assets [Member] | Aluminum Contracts [Member] | Level 1 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives   3  
Derivatives Designated as Hedging Instruments [Member] | Other Noncurrent Assets [Member] | Interest Rate Contracts [Member] | Level 2 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 30 37  
Derivatives Designated as Hedging Instruments [Member] | Other Noncurrent Assets [Member] | Energy Contracts [Member] | Level 3 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 4 3  
Derivatives Not Designated as Hedging Instruments [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 373 541  
Derivatives Not Designated as Hedging Instruments [Member] | Prepaid Expenses and Other Current Assets [Member] | Aluminum Contracts [Member] | Level 3 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 175 211  
Derivatives Not Designated as Hedging Instruments [Member] | Other Noncurrent Assets [Member] | Aluminum Contracts [Member] | Level 3 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 198 329  
Derivatives Not Designated as Hedging Instruments [Member] | Other Noncurrent Assets [Member] | Foreign Exchange Contracts [Member] | Level 1 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives   1  
Margin Held [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 7 26  
Margin Held [Member] | Prepaid Expenses and Other Current Assets [Member] | Aluminum Contracts [Member] | Level 1 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives   9  
Margin Held [Member] | Prepaid Expenses and Other Current Assets [Member] | Interest Rate Contracts [Member] | Level 2 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives 6 8  
Margin Held [Member] | Other Noncurrent Assets [Member] | Interest Rate Contracts [Member] | Level 2 [Member]
      
Derivative Instruments, Gain (Loss) [Line Items]      
Fair value asset derivatives $ 1 $ 9