REVENUE - Passenger Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Total Operating Revenue	$ 3,766	$ 3,072	$ 10,607	$ 8,201
Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	3,424	2,821	9,587	7,476
Passenger revenue | Domestic
Disaggregation of Revenue [Line Items]
Total Operating Revenue	3,202	2,685	8,725	6,980
Passenger revenue | Latin America
Disaggregation of Revenue [Line Items]
Total Operating Revenue	100	118	480	478
Passenger revenue | Pacific
Disaggregation of Revenue [Line Items]
Total Operating Revenue	122	18	382	18
Passenger ticket revenue, net of taxes and fees | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	2,889	2,380	8,073	6,254
Passenger ancillary revenue | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	177	152	479	395
Loyalty program passenger revenue | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	$ 358	$ 289	$ 1,035	$ 827