REVENUE FROM CONTRACTS WITH CUSTOMERS - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Deferred Revenue Arrangement [Line Items]
Receivable	$ 384		$ 383
Costs and Expenses	2,398	$ 2,382
Mileage Plan Revenue [Member]
Deferred Revenue Arrangement [Line Items]
Contract liability revenue recognized	292	285
Receivable	104		$ 102
Mileage Plan Revenue [Member] | Mileage plan other revenue [Member]
Deferred Revenue Arrangement [Line Items]
Contract liability revenue recognized	(28)	(21)
Passenger Revenue [Member]
Deferred Revenue Arrangement [Line Items]
Contract liability revenue recognized	$ 584	$ 485