Comprehensive Income (Loss) - Schedule of AOCI Components (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 10,789	$ 10,687
Changes in fair value	181	(72)
Reclassification to earnings	(38)	(71)
Balance at end of period	11,054	11,054
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	58	344
Balance at end of period	201	201
Fuel and Interest Rate Derivatives | Fuel derivative contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(65)	305
Changes in fair value	228	(101)
Reclassification to earnings	(52)	(93)
Balance at end of period	111	111
Fuel and Interest Rate Derivatives | Interest rate derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(29)	(32)
Changes in fair value	8	8
Reclassification to earnings	2	5
Balance at end of period	(19)	(19)
Defined benefit plan items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	170	170
Balance at end of period	170	170
Deferred tax impact
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(18)	(99)
Changes in fair value	(55)	21
Reclassification to earnings	12	17
Balance at end of period	$ (61)	$ (61)