Revenue Recognition - Revenue by Geographic Region (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
Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	5,894	1,264	9,262	7,531
Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	467	119	734	1,113
Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	586	26	967	889
Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	179	59	313	527
Passenger
Disaggregation of Revenue [Line Items]
Operating revenue	5,339	678	8,087	8,247
Passenger | Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	4,478	564	6,758	6,165
Passenger | Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	288	64	430	882
Passenger | Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	485	18	749	783
Passenger | Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	$ 88	$ 32	$ 150	$ 417