Revenue - Roll Forward of Frequent Flyer Deferred Revenue (Details) - Frequent Flyer - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Frequent Flyer Deferred Revenue [Roll Forward]
Total Frequent flyer deferred revenue - beginning balance	$ 5,488	$ 5,138	$ 5,276	$ 5,005
Total miles awarded	228	682	787	1,289
Travel miles redeemed (Passenger revenue)	(34)	(589)	(356)	(1,027)
Non-travel miles redeemed (Other operating revenue)	(12)	(33)	(37)	(69)
Total Frequent flyer deferred revenue - ending balance	$ 5,670	$ 5,198	$ 5,670	$ 5,198