REVENUE - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Dec. 31, 2024
Disaggregation of Revenue [Line Items]
Receivables - net	$ 737		$ 737		$ 558
Passenger revenue
Disaggregation of Revenue [Line Items]
Revenue recognized	228	$ 150	1,100	$ 717
Mileage Plan Revenue
Disaggregation of Revenue [Line Items]
Receivables - net	$ 306		$ 306		$ 176