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Supplemental Financial Information - Accrued Liabilities (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Accrued Liabilities, Current [Abstract]    
Retirement plans $ 144 $ 135
Aircraft rentals 109 139
Vacation pay 275 270
Health 62 70
Workers compensation 158 159
Accrued taxes 58 67
Other 198 212
Accrued liabilities 1,004 1,102
Fuel derivatives | Accrued Liabilities
   
Accrued Liabilities, Current [Abstract]    
Liability derivative contracts, net $ 0 $ 50