Financial Derivative Instruments - Location and Amount Recognized in Income by Hedging Relationship (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Cash Flow Hedging
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	$ (1)	$ 127
Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	(1)	125
Cash Flow Hedging | Other
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	0	2
Fuel and oil
Derivative [Line Items]
Derivatives designated as hedging instruments	22	(28)
Fuel and oil | Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	22	(28)
Fuel and oil | Cash Flow Hedging | Other
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	0	0
Other operating expenses
Derivative [Line Items]
Derivatives designated as hedging instruments	2	2
Other operating expenses | Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	0	0
Other operating expenses | Cash Flow Hedging | Other
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	$ 2	$ 2