Revenue - Roll Forward of Frequent Flyer Deferred Revenue (Details) - Frequent Flyer - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Frequent Flyer Deferred Revenue [Roll Forward]
Total Frequent flyer deferred revenue - beginning balance	$ 5,198	$ 4,989	$ 5,005	$ 4,783
Miles awarded	662	616	1,951	1,826
Travel miles redeemed (Passenger revenue)	(607)	(580)	(1,634)	(1,508)
Non-travel miles redeemed (Other operating revenue)	(34)	(38)	(103)	(114)
Total Frequent flyer deferred revenue - ending balance	$ 5,219	$ 4,987	$ 5,219	$ 4,987