Revenue - Air Traffic Liability Rollforward (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Air Traffic Liability Roll Forward
ATL, beginning balance	$ 5,510	$ 5,070
Current Period Sales	5,946	11,178
Revenue amounts in beginning balance	(1,936)	(2,855)
Revenue from Current Period Sales	(2,641)	(7,409)
ATL, ending balance	$ 6,879	$ 5,984