Revenue Recognition - Revenue by Geographic Region (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Operating revenue	$ 4,150	$ 8,592
Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	3,368	6,267
Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	267	994
Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	381	863
Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	134	468
Passenger
Disaggregation of Revenue [Line Items]
Operating revenue	2,748	7,569
Passenger | Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	2,280	5,601
Passenger | Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	142	818
Passenger | Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	264	765
Passenger | Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	$ 62	$ 385