REVENUE - Passenger Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Disaggregation of Revenue [Line Items]
Total Operating Revenue	$ 4,065	$ 3,704	$ 7,365	$ 6,841
Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	3,644	3,355	6,564	6,163
Passenger revenue | Domestic
Disaggregation of Revenue [Line Items]
Total Operating Revenue	3,336	3,061	5,935	5,523
Passenger revenue | Latin America
Disaggregation of Revenue [Line Items]
Total Operating Revenue	131	166	318	380
Passenger revenue | Pacific
Disaggregation of Revenue [Line Items]
Total Operating Revenue	137	128	271	260
Passenger revenue | Atlantic
Disaggregation of Revenue [Line Items]
Total Operating Revenue	40	0	40	0
Passenger ticket revenue, net of taxes and fees | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	3,079	2,832	5,505	5,184
Passenger ancillary revenue | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	177	162	324	302
Loyalty program passenger revenue | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	$ 388	$ 361	$ 735	$ 677