Revenue - Air Traffic Liability - Loyalty Program Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Change in Contract With Customer, Liability [Roll Forward]
Beginning balance	$ 4,623	$ 3,561	$ 4,447	$ 3,385
Amounts deferred associated with points awarded	656	385	1,121	1,041
Ending balance	4,719	3,856	4,719	3,856
Passenger Customer
Change in Contract With Customer, Liability [Roll Forward]
Revenue recognized from points redeemed	(549)	(81)	(826)	(542)
Other
Change in Contract With Customer, Liability [Roll Forward]
Revenue recognized from points redeemed	$ (11)	$ (9)	$ (23)	$ (28)