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Derivatives and Other Financial Instruments - Schedule of Fair Values of Outstanding Derivative Contracts Recorded as Assets (Detail) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives $ 688 $ 94
Level 1 [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 48 57
Level 3 [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 615 12
Level 2 [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 48 47
Other Noncurrent Assets [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 23 [1] 22 [1]
Derivatives Designated as Hedging Instruments [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 100 109
Derivatives Designated as Hedging Instruments [Member] | Prepaid Expense And Other Current Assets [Member] | Aluminum Contracts [Member] | Level 1 [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 38 51
Derivatives Designated as Hedging Instruments [Member] | Prepaid Expense And Other Current Assets [Member] | Aluminum Contracts [Member] | Level 3 [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 6 5
Derivatives Designated as Hedging Instruments [Member] | Prepaid Expense And Other Current Assets [Member] | Interest Rate Contract [Member] | Level 2 [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 5 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 8 6
Derivatives Designated as Hedging Instruments [Member] | Other Noncurrent Assets [Member] | Interest Rate Contract [Member] | Level 2 [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 43 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   2
Derivatives Not Designated as Hedging Instrument [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 611 [2] 7 [2]
Derivatives Not Designated as Hedging Instrument [Member] | Prepaid Expense And Other Current Assets [Member] | Aluminum Contracts [Member] | Level 3 [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 208 [2]  
Derivatives Not Designated as Hedging Instrument [Member] | Prepaid Expense And Other Current Assets [Member] | Aluminum Contracts [Member] | Level 2 [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives   1 [2]
Derivatives Not Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member] | Aluminum Contracts [Member] | Level 3 [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 401 [2] 5 [2]
Derivatives Not Designated as Hedging Instrument [Member] | Other Noncurrent Assets [Member] | Foreign Exchange Contract [Member] | Level 1 [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 2 [2] 1 [2]
Margin Held [Member] | Prepaid Expense And Other Current Assets [Member] | Aluminum Contracts [Member] | Level 1 [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 4 [1] 7 [1]
Margin Held [Member] | Prepaid Expense And Other Current Assets [Member] | Interest Rate Contract [Member] | Level 2 [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives 5 [1] 8 [1]
Margin Held [Member] | Other Noncurrent Assets [Member] | Interest Rate Contract [Member] | Level 2 [Member]
    
Derivative Instruments, Gain (Loss) [Line Items]    
Fair value asset derivatives $ 14 [1] $ 7 [1]
[1] All margin held is in the form of cash and is valued under a Level 1 technique. The levels that correspond to the margin held in the table above reference the level of the corresponding asset for which it is held. Alcoa elected to net the margin held against the fair value amounts recognized for derivative instruments executed with the same counterparties under master netting arrangements.
[2] See the "Other" section within Note N for additional information on Alcoa's purpose for entering into derivatives not designated as hedging instruments and its overall risk management strategies.