Revenue - Roll Forward of Frequent Flyer Deferred Revenue (Details) - Frequent Flyer - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Frequent Flyer Deferred Revenue [Roll Forward]
Total Frequent flyer deferred revenue - beginning balance	$ 5,670	$ 5,198	$ 5,276	$ 5,005
Total miles awarded	268	662	1,056	1,951
Travel miles redeemed (Passenger revenue)	(87)	(607)	(444)	(1,634)
Non-travel miles redeemed (Other operating revenue)	(16)	(34)	(53)	(103)
Total Frequent flyer deferred revenue - ending balance	$ 5,835	$ 5,219	$ 5,835	$ 5,219