Revenue Recognition - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
General terms of validity for passenger tickets and credits from date of original ticket issuance	1 year
Total value of refunds to customers	$ 850
Cash sales of mileage credits	$ 992	$ 980
Majority of new miles redemption period (in years)	2 years
Air traffic
Disaggregation of Revenue [Line Items]
Revenue recognized that was previously deferred	$ 2,800