Revenue Recognition - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Total value of refunds to customers		$ 3,100
Travel credits as a percentage of air traffic liability	65.00%	65.00%
Revenue recognized that was in prior year air traffic liability		$ 3,100	$ 3,800	$ 3,500
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		$ 2,800	4,200	3,500
Proceeds from issuance of debt		$ 22,790	$ 2,057	$ 3,745
Majority of new miles, redemption period (in years)		2 years
Secured Debt | SkyMiles program
Disaggregation of Revenue [Line Items]
Proceeds from issuance of debt	$ 9,000