Revenue Recognition - Passenger Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Operating revenue	$ 17,095	$ 47,007	$ 44,438
Passenger
Disaggregation of Revenue [Line Items]
Operating revenue	12,883	42,277	39,755
Ticket
Disaggregation of Revenue [Line Items]
Operating revenue	10,970	36,908	34,950
Loyalty travel awards
Disaggregation of Revenue [Line Items]
Operating revenue	935	2,900	2,651
Travel-related services
Disaggregation of Revenue [Line Items]
Operating revenue	$ 978	$ 2,469	$ 2,154