REVENUE RECOGNITION - Revenue by Geographic Region (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Operating revenue	$ 13,748	$ 12,759
Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	10,031	9,396
Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	1,581	1,548
Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	1,442	1,280
Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	694	535
Passenger
Disaggregation of Revenue [Line Items]
Operating revenue	11,131	10,411
Passenger | Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	7,983	7,594
Passenger | Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	1,305	1,244
Passenger | Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	1,265	1,132
Passenger | Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	$ 578	$ 441