ACCUMULATED OTHER COMPREHENSIVE INCOME - Schedule of AOCI Components (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 10,687	$ 10,414
Changes in fair value	(240)	590
Reclassification to earnings	(104)	(634)
Balance at end of period	10,515	10,687
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	344	388
Balance at end of period	0	344
Fuel and Interest Rate Derivatives | Fuel derivative contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	305	492
Changes in fair value	(312)	645
Reclassification to earnings	(128)	(832)
Balance at end of period	(135)	305
Fuel and Interest Rate Derivatives | Interest rate derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(32)	(57)
Changes in fair value	10	18
Reclassification to earnings	7	7
Balance at end of period	(15)	(32)
Defined benefit plan items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	170	66
Changes in fair value	(11)	106
Reclassification to earnings	(10)	(2)
Balance at end of period	149	170
Deferred tax impact
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(99)	(113)
Changes in fair value	73	(179)
Reclassification to earnings	27	193
Balance at end of period	$ 1	$ (99)