REVENUE - Passenger Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Disaggregation of Revenue [Line Items]
Total Operating Revenue	$ 3,300	$ 3,137
Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	2,920	2,808
Passenger revenue | Domestic
Disaggregation of Revenue [Line Items]
Total Operating Revenue	2,599	2,462
Passenger revenue | Latin America
Disaggregation of Revenue [Line Items]
Total Operating Revenue	187	214
Passenger revenue | Pacific
Disaggregation of Revenue [Line Items]
Total Operating Revenue	134	132
Passenger ticket revenue, net of taxes and fees | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	2,426	2,352
Passenger ancillary revenue | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	147	140
Loyalty program passenger revenue | Passenger revenue
Disaggregation of Revenue [Line Items]
Total Operating Revenue	$ 347	$ 316