REVENUE FROM CONTRACTS WITH CUSTOMERS - Contract Liabilities Activity (Details) - Mileage Plan Revenue [Member] - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Change in Contract with Customer, Liability [Roll Forward]
Total Deferred Revenue balance at January 1	$ 2,603	$ 2,497
Revenue recognized	613	602
Total Deferred Revenue balance at Sept 30	2,641	2,577
Passenger revenue [Member]
Change in Contract with Customer, Liability [Roll Forward]
Revenue recognized	(508)	(470)
Mileage plan other revenue [Member]
Change in Contract with Customer, Liability [Roll Forward]
Revenue recognized	$ (67)	$ (52)