Revenue - Air Traffic Liability Rollforward (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Air Traffic Liability Roll Forward
ATL, beginning balance	$ 5,510	$ 5,070
Current Period Sales	4,565	5,704
Revenue amounts in beginning balance	(1,949)	(2,008)
Revenue from Current Period Sales	(1,915)	(2,752)
ATL, ending balance	$ 6,211	$ 6,014