Impact of the COVID-19 Pandemic - Fleet Retirements by Aircraft Type (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) aircraft
Aircraft retirement decisions
Number of aircraft | aircraft		383
Impairment-related charge		$ 4,409
777
Aircraft retirement decisions
Number of aircraft | aircraft		18
Impairment-related charge		$ 1,440
767-300ER
Aircraft retirement decisions
Number of aircraft | aircraft		56
Impairment-related charge		$ 1,084
717
Aircraft retirement decisions
Number of aircraft | aircraft		91
Impairment-related charge		$ 950
MD-90
Aircraft retirement decisions
Number of aircraft | aircraft		26
Impairment-related charge		$ 335
CRJ-200
Aircraft retirement decisions
Number of aircraft | aircraft		125
Impairment-related charge		$ 320
737-700
Aircraft retirement decisions
Number of aircraft | aircraft		10
Impairment-related charge		$ 223
A-320
Aircraft retirement decisions
Number of aircraft | aircraft		10
Impairment-related charge		$ 57
MD-88
Aircraft retirement decisions
Number of aircraft | aircraft		47
Impairment-related charge		$ 0
Accelerated depreciation	$ 22