Revenue - Air Traffic Liability - Loyalty Program Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Movement in Deferred Revenue
Air traffic liability - loyalty program - beginning balance	$ 3,385	$ 3,011
Amounts deferred associated with points awarded	1,958	2,941
Revenue recognized from points redeemed - Passenger	(1,003)	(2,487)
Revenue recognized from points redeemed - Other	(60)	(80)
Unused funds converted to loyalty points	167	0
Air traffic liability - loyalty program - ending balance	$ 4,447	$ 3,385