Revenue - Air Traffic Liability Rollforward (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Air Traffic Liability Roll Forward
ATL, beginning balance	$ 5,070	$ 4,565
Current Period Sales	11,178	10,927
Revenue amounts in beginning balance	(2,855)	(2,613)
Revenue from Current Period Sales	(7,409)	(7,349)
ATL, ending balance	$ 5,984	$ 5,530