ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Reclassifications (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	$ 5,812	$ 6,217	$ 5,975
Less: Tax expense	133	168	189
Other (gains) losses, net	4	(62)	12
Other operating expenses	4,138	3,999	3,735
Net income	465	$ 465	$ 539
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	55
Defined benefit plan items | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Less: Tax expense	(2)
Other (gains) losses, net	(7)
Net income	(5)
Fuel derivative contracts | Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Fuel and oil	72
Less: Tax expense	17
Net income	55
Other | Fuel derivatives | Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Less: Tax expense	3
Other operating expenses	8
Net income	$ 5