Comprehensive Income (Loss) - Schedule of AOCI Components (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 10,302	$ 10,687
Changes in fair value	(125)	(252)
Reclassification to earnings	(14)	(34)
Balance at end of period	10,789	10,789
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	197	344
Balance at end of period	58	58
Fuel and Interest Rate Derivatives | Fuel derivative contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	114	305
Changes in fair value	(165)	(328)
Reclassification to earnings	(14)	(42)
Balance at end of period	(65)	(65)
Fuel and Interest Rate Derivatives | Interest rate derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(32)	(32)
Changes in fair value	1	0
Reclassification to earnings	2	3
Balance at end of period	(29)	(29)
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	(55)	(99)
Changes in fair value	39	76
Reclassification to earnings	(2)	5
Balance at end of period	$ (18)	$ (18)