REVENUE - Passenger Revenue Breakout (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue
Total operating revenues	$ 26,091	$ 23,814	$ 15,790
Passenger
Disaggregation of Revenue
Total operating revenues	23,637	21,408	14,066
Passenger non-loyalty
Disaggregation of Revenue
Total operating revenues	19,073	17,645	11,377
Passenger loyalty - air transportation
Disaggregation of Revenue
Total operating revenues	3,639	3,028	2,136
Passenger ancillary sold separately
Disaggregation of Revenue
Total operating revenues	$ 925	$ 735	$ 553