REVENUE - Passenger Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Revenue	$ 11,735	$ 10,426	$ 9,646
Passenger Revenue
Disaggregation of Revenue [Line Items]
Revenue	10,654	9,526	8,808
Passenger Revenue | Domestic
Disaggregation of Revenue [Line Items]
Revenue	9,831	8,938	8,326
Passenger Revenue | Latin America
Disaggregation of Revenue [Line Items]
Revenue	677	588	482
Passenger Revenue | Pacific
Disaggregation of Revenue [Line Items]
Revenue	146	0	0
Passenger ticket revenue, net of taxes and fees | Passenger Revenue
Disaggregation of Revenue [Line Items]
Revenue	8,926	8,016	7,430
Passenger ancillary revenue | Passenger Revenue
Disaggregation of Revenue [Line Items]
Revenue	548	476	447
Loyalty program passenger revenue | Passenger Revenue
Disaggregation of Revenue [Line Items]
Revenue	$ 1,180	$ 1,034	$ 931