Revenue Recognition - Passenger Revenue (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Operating revenue	$ 11,439	$ 12,560	$ 12,536	$ 10,472	$ 10,742	$ 11,953	$ 11,775	$ 9,968	$ 47,007	$ 44,438	$ 41,138
Passenger
Disaggregation of Revenue [Line Items]
Operating revenue									42,277	39,755	36,947
Ticket
Disaggregation of Revenue [Line Items]
Operating revenue									36,908	34,950	32,467
Loyalty travel awards
Disaggregation of Revenue [Line Items]
Operating revenue									2,900	2,651	2,403
Travel-related services
Disaggregation of Revenue [Line Items]
Operating revenue									$ 2,469	$ 2,154	$ 2,077