REVENUE - Passenger Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Disaggregation of Revenue [Line Items]
Total Operating Revenue	$ 4,308	$ 3,766	$ 11,673	$ 10,607
Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	3,885	3,424	10,449	9,587
Passenger revenue | Domestic
Disaggregation of Revenue [Line Items]
Total Operating Revenue	3,586	3,202	9,521	8,725
Passenger revenue | Latin America
Disaggregation of Revenue [Line Items]
Total Operating Revenue	85	100	403	480
Passenger revenue | Pacific
Disaggregation of Revenue [Line Items]
Total Operating Revenue	141	122	412	382
Passenger revenue | Atlantic
Disaggregation of Revenue [Line Items]
Total Operating Revenue	73	0	113	0
Passenger ticket revenue, net of taxes and fees | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	3,296	2,889	8,801	8,073
Passenger ancillary revenue | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	202	177	526	479
Loyalty program passenger revenue | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	$ 387	$ 358	$ 1,122	$ 1,035