SPECIAL ITEMS - Operating And Non-Operating (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Unusual or Infrequent Item, or Both [Line Items]
Special items - operating	$ 345	$ 443	$ 580
Special items - net non-operating	16	(18)	0
Fleet transition
Unusual or Infrequent Item, or Both [Line Items]
Special items - operating	11	385	481
Labor agreements
Unusual or Infrequent Item, or Both [Line Items]
Special items - operating	73	51	84
Integration costs
Unusual or Infrequent Item, or Both [Line Items]
Special items - operating	208	7	0
Legal and professional fees
Unusual or Infrequent Item, or Both [Line Items]
Special items - operating	115	7
Employee-related and other merger costs
Unusual or Infrequent Item, or Both [Line Items]
Special items - operating	93	0
Litigation
Unusual or Infrequent Item, or Both [Line Items]
Special items - operating	$ 53	$ 0	$ 15