Revenue Recognition - Passenger Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Operating revenue	$ 7,126	$ 1,468	$ 11,276	$ 10,060
Passenger
Disaggregation of Revenue [Line Items]
Operating revenue	5,339	678	8,087	8,247
Ticket
Disaggregation of Revenue [Line Items]
Operating revenue	4,553	568	6,830	7,078
Loyalty travel awards
Disaggregation of Revenue [Line Items]
Operating revenue	428	45	669	588
Travel-related services
Disaggregation of Revenue [Line Items]
Operating revenue	$ 358	$ 65	$ 588	$ 581