REVENUE RECOGNITION - Revenue by Geographic Region (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Disaggregation of Revenue [Line Items]
Operating revenue	$ 15,488	$ 13,975	$ 43,825	$ 37,147
Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	10,461	10,118	30,607	28,322
Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	3,497	2,705	8,223	5,538
Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	891	752	3,208	2,417
Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	639	400	1,787	870
Passenger
Disaggregation of Revenue [Line Items]
Operating revenue	13,119	11,464	36,735	29,329
Passenger | Domestic
Disaggregation of Revenue [Line Items]
Operating revenue	8,662	8,154	25,200	22,035
Passenger | Atlantic
Disaggregation of Revenue [Line Items]
Operating revenue	3,110	2,313	7,157	4,553
Passenger | Latin America
Disaggregation of Revenue [Line Items]
Operating revenue	788	659	2,846	2,084
Passenger | Pacific
Disaggregation of Revenue [Line Items]
Operating revenue	$ 559	$ 338	$ 1,532	$ 657