REVENUE - Loyalty Program Liability Rollforward (Details) - Mileage Plan Revenue - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Change in Contract with Customer, Liability [Roll Forward]
Beginning balance	$ 2,603	$ 2,497
Deferred revenue acquired from Hawaiian as of September 18	537	0
Increase in liability for mileage credits issued	1,400	1,197
Ending balance	3,256	2,603
Passenger Services [Member]
Change in Contract with Customer, Liability [Roll Forward]
Revenue recognized	(1,124)	(974)
Mileage Plan Services, Other
Change in Contract with Customer, Liability [Roll Forward]
Revenue recognized	$ (160)	$ (117)