REVENUE - Loyalty Program Liability Rollforward (Details) - Mileage Plan Revenue - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Change in Contract with Customer, Liability [Roll Forward]
Beginning balance	$ 3,256	$ 2,603
Increase in liability for mileage credits issued	414	292
Ending balance	3,314	2,633
Passenger Services
Change in Contract with Customer, Liability [Roll Forward]
Revenue recognized	(307)	(234)
Mileage plan other revenue
Change in Contract with Customer, Liability [Roll Forward]
Revenue recognized	$ (49)	$ (28)