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Fuel - Derivative Assets (Details) (Designated as Hedging Instrument, USD $)
In Millions, unless otherwise specified
Sep. 30, 2012
Dec. 31, 2011
Derivatives, Fair Value [Line Items]    
Derivatives, gross $ 0 $ 24
Fuel Contracts | Other Current Assets
   
Derivatives, Fair Value [Line Items]    
Derivatives, gross $ 0 $ 24