REVENUE - Passenger Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Total Operating Revenue	$ 3,137	$ 2,232
Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	2,808	2,004
Passenger revenue | Domestic
Disaggregation of Revenue [Line Items]
Total Operating Revenue	2,462	1,805
Passenger revenue | Latin America
Disaggregation of Revenue [Line Items]
Total Operating Revenue	214	199
Passenger revenue | Pacific
Disaggregation of Revenue [Line Items]
Total Operating Revenue	132	0
Passenger ticket revenue, net of taxes and fees | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	2,352	1,648
Passenger ancillary revenue | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	140	108
Loyalty program passenger revenue | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	$ 316	$ 248