Comprehensive Loss - Schedule of AOCI Components (Details) $ in Millions	3 Months Ended
	Mar. 31, 2024 USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 10,515
Changes in fair value	1
Reclassification to earnings	18
Balance at end of period	10,196
Accumulated other comprehensive income (loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	0
Balance at end of period	19
Fuel and Interest Rate Derivatives | Fuel derivative contracts
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(135)
Changes in fair value	1
Reclassification to earnings	22
Balance at end of period	(112)
Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(15)
Changes in fair value	0
Reclassification to earnings	2
Balance at end of period	(13)
Defined benefit plan items
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	149
Changes in fair value	0
Reclassification to earnings	0
Balance at end of period	149
Deferred tax impact
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	1
Changes in fair value	0
Reclassification to earnings	(6)
Balance at end of period	$ (5)