Revenue Recognition - Narrative (Details) - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue recognized that was previously recorded in air traffic liability	$ 2.2	$ 3.1	$ 3.8
Total value of cash refunds to customers	$ 1.1	$ 3.1
Travel credits as a percentage of air traffic liability	45.00%	65.00%
Marketing contracts initial terms, minimum (in years)	3 years
Marketing contracts initial terms, maximum (in years)	11 years
Cash sales of miles from marketing agreements	$ 4.1	$ 2.9	$ 4.2
Majority of new miles, redemption period (in years)	2 years