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Schedule of Gains (Losses) on Derivative Instruments (Detail) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2013
Mar. 31, 2012
Designated as Hedging Instrument | Cash Flow Hedging
   
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of Gain (Loss) Recognized in AOCI on Derivatives (Effective Portion) $ (9) $ 93
Gain (Loss) Reclassified from AOCI into Income (Fuel Expense) (Effective Portion) (9) (31)
Amount of Gain (Loss) Recognized in Income (Nonoperating Expense) (Ineffective Portion)   25
Not Designated as Hedging Instrument
   
Derivative Instruments, Gain (Loss) [Line Items]    
Amount of Gain (Loss) Recognized in Income (Nonoperating Expense) $ 50