REVENUE FROM CONTRACTS WITH CUSTOMERS - Contract Liabilities Activity (Details) - Mileage Plan Revenue [Member] - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Change in Contract with Customer, Liability [Roll Forward]
Total Deferred Revenue balance at January 1	$ 2,497	$ 2,358
Revenue recognized	602	518
Total Deferred Revenue balance at Sept 30	2,577	2,441
Passenger revenue [Member]
Change in Contract with Customer, Liability [Roll Forward]
Revenue recognized	(470)	(409)
Mileage plan other revenue [Member]
Change in Contract with Customer, Liability [Roll Forward]
Revenue recognized	$ (52)	$ (26)