SUPPLEMENTAL FINANCIAL INFORMATION - Accrued Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Accrued Liabilities, Current [Abstract]
Voluntary Separation Program (c)	$ 65	$ 72
Profitsharing and savings plans	141	167
Vacation pay	516	484
Health	163	261
Workers compensation	133	164
Property and income taxes	63	37
Interest	34	45
Contract labor and non-contract incentive accruals	2,022	563
Other	469	250
Accrued liabilities	3,606	$ 2,043
Unusual or Infrequent Item, or Both [Line Items]
Incremental expense	534
Flight Attendant
Unusual or Infrequent Item, or Both [Line Items]
Incremental expense	180
Pilots
Unusual or Infrequent Item, or Both [Line Items]
Incremental expense	$ 354