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Revenue Recognition - Passenger Revenue (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Disaggregation of Revenue [Line Items]    
Operating revenue $ 10,472 $ 9,968
Passenger    
Disaggregation of Revenue [Line Items]    
Operating revenue 9,254 8,765
Ticket    
Disaggregation of Revenue [Line Items]    
Operating revenue 7,988 7,653
Loyalty travel awards    
Disaggregation of Revenue [Line Items]    
Operating revenue 692 618
Travel-related services    
Disaggregation of Revenue [Line Items]    
Operating revenue $ 574 $ 494