REVENUE FROM CONTRACTS WITH CUSTOMERS Contract Liabilities Activity (Details) - Mileage Plan Revenue [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Contract with Customer, Liability	$ 2,603	$ 2,497	$ 2,358
Contract with Customer, Liability, Increase From Issuance of Credits	1,197	1,082
Mileage Plan Services, Other [Member]
Contract with Customer, Liability, Revenue Recognized	(117)	(65)
Passenger Services [Member]
Contract with Customer, Liability, Revenue Recognized	$ (974)	$ (878)