Financial Derivative Instruments - Location and Amount Recognized in Income by Hedging Relationship (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Cash Flow Hedging
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	$ 61	$ (182)	$ 83	$ 71
Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	61	(175)	83	78
Cash Flow Hedging | Other
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	0	(7)	0	(7)
Fuel and oil
Derivative [Line Items]
Total	15	(52)	54	(93)
Fuel and oil | Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	15	(52)	54	(93)
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	6	5
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	$ 6	$ 5