Revenue - Roll Forward of Frequent Flyer Deferred Revenue (Details) - Frequent Flyer - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Frequent Flyer Deferred Revenue [Roll Forward]
Total Frequent flyer deferred revenue - beginning balance	$ 5,276	$ 5,005
Total miles awarded	559	607
Travel miles redeemed (Passenger revenue)	(322)	(438)
Non-travel miles redeemed (Other operating revenue)	(25)	(36)
Total Frequent flyer deferred revenue - ending balance	$ 5,488	$ 5,138