Comprehensive Income - Schedule of AOCI Components (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2024
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 10,196	$ 10,515
Changes in fair value	(23)	(22)
Reclassification to earnings	15	33
Balance at end of period	10,465	10,465
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	19	0
Balance at end of period	11	11
Fuel derivatives | Fuel derivative contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(112)	(135)
Changes in fair value	(30)	(29)
Reclassification to earnings	17	39
Balance at end of period	(125)	(125)
Defined benefit plan items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	149	149
Changes in fair value	0	0
Reclassification to earnings	0	0
Balance at end of period	149	149
Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(13)	(15)
Changes in fair value	0	0
Reclassification to earnings	2	4
Balance at end of period	(11)	(11)
Deferred tax impact
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(5)	1
Changes in fair value	7	7
Reclassification to earnings	(4)	(10)
Balance at end of period	$ (2)	$ (2)