Financial Derivative Instruments - Location and Amount Recognized in Income by Hedging Relationship (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Cash Flow Hedging
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	$ 23	$ 125	$ 22	$ 252
Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	23	126	22	252
Cash Flow Hedging | Other
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	0	(1)	0	0
Fuel and oil
Derivative [Line Items]
Total	17	(14)	39	(42)
Fuel and oil | Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	17	(14)	39	(42)
Fuel and oil | Cash Flow Hedging | Other
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	0	0	0	0
Other operating expenses
Derivative [Line Items]
Total	2	2	4	3
Other operating expenses | Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	0	0	0	0
Other operating expenses | Cash Flow Hedging | Other
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	$ (2)	$ (2)	$ (4)	$ (3)