REVENUE FROM CONTRACTS WITH CUSTOMERS - Contract Liabilities Activity (Details) - Mileage Plan Revenue [Member] - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Change in Contract with Customer, Liability [Roll Forward]
Total Deferred Revenue balance at January 1	$ 2,497	$ 2,358
Revenue recognized	285	259
Total Deferred Revenue balance at Sept 30	2,543	2,432
Passenger revenue [Member]
Change in Contract with Customer, Liability [Roll Forward]
Revenue recognized	(218)	(176)
Mileage plan other revenue [Member]
Change in Contract with Customer, Liability [Roll Forward]
Revenue recognized	$ (21)	$ (9)