Revenue - Roll Forward of Frequent Flyer Deferred Revenue (Details) - Frequent Flyer - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Frequent Flyer Deferred Revenue [Roll Forward]
Total Frequent flyer deferred revenue - beginning balance	$ 6,109	$ 5,488	$ 5,975	$ 5,276
Total miles awarded	360	228	632	787
Travel miles redeemed (Passenger revenue)	(267)	(34)	(390)	(356)
Non-travel miles redeemed (Other operating revenue)	(17)	(12)	(32)	(37)
Total Frequent flyer deferred revenue - ending balance	$ 6,185	$ 5,670	$ 6,185	$ 5,670