Revenue Recognition - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2020	Jun. 30, 2019	Dec. 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	$ 1,300		$ 2,100
Revenue recognized that was previously deferred			2,900
Cash sales of mileage credits			$ 1,500	$ 2,000
Majority of new miles redemption period (in years)			2 years
Air traffic
Disaggregation of Revenue [Line Items]
Deferred revenue liability, noncurrent	$ 315		$ 315		$ 0