REVENUE FROM CONTRACTS WITH CUSTOMERS - Disaggregation of Revenue (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax	$ 95	$ 3,072	$ 2,839	$ 8,201	$ 7,873
Passenger [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,821	2,618	7,476	7,200
Mileage plan other revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		171	159	509	483
Passenger Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,821	2,618	7,476	7,200
Passenger Revenue [Member] | Passenger ticket revenue, including ticket breakage and net of taxes and fees [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,380	2,226	6,254	6,081
Passenger Revenue [Member] | Passenger ancillary revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		152	135	395	362
Passenger Revenue [Member] | Mileage Plan passenger revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		289	257	827	757
Passenger Revenue [Member] | Passenger [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		2,821	2,618	7,476	7,200
Mileage Plan Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		460	416	1,336	1,240
Mileage Plan Revenue [Member] | Passenger ticket revenue, including ticket breakage and net of taxes and fees [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		289	257	827	757
Mileage Plan Revenue [Member] | Mileage plan other revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		171	159	509	483
Cargo and Other Revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		80	62	216	190
Cargo and Other Revenue [Member] | Cargo revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		43	29	107	97
Cargo and Other Revenue [Member] | Other revenue [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		$ 37	$ 33	$ 109	$ 93