Revenue - Air Traffic Liability Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Air Traffic Liability Rollforward [Abstract]
ATL, beginning balance	$ 5,070	$ 4,565
Current Period Sales	21,296	21,026
Revenue amounts in beginning balance	(3,816)	(3,479)
Revenue from Current Period Sales	(17,040)	(17,042)
ATL, ending balance	$ 5,510	$ 5,070