Revenue Recognition - Revenue by Geographic Region (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
Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	13,339	33,382	31,309
Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	1,649	7,308	7,012
Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	1,321	3,326	3,157
Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	786	2,991	2,960
Passenger
Disaggregation of Revenue [Line Items]
Operating revenue	12,883	42,277	39,755
Passenger | Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	10,041	30,465	28,235
Passenger | Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	1,171	6,326	6,135
Passenger | Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	1,113	2,985	2,864
Passenger | Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	$ 558	$ 2,501	$ 2,521