Financial Derivative Instruments - Location and Amount Recognized in Income by Hedging Relationship (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2022	Dec. 31, 2021
Cash Flow Hedging
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	$ (508)	$ (463)
Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	(494)	(461)
Cash Flow Hedging | Interest rate derivatives
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	$ (14)	$ (2)
Fuel and oil
Derivative [Line Items]
Derivatives designated as hedging instruments			$ (832)	$ 4
Fuel and oil | Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income			(832)	4
Fuel and oil | Cash Flow Hedging | Interest rate derivatives
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			7
Other operating expenses | Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income			0
Other operating expenses | Cash Flow Hedging | Interest rate derivatives
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income			$ 7
Other (gains)/losses, net
Derivative [Line Items]
Derivatives designated as hedging instruments				6
Other (gains)/losses, net | Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income				6
Other (gains)/losses, net | Cash Flow Hedging | Interest rate derivatives
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income				0
Other operating expenses
Derivative [Line Items]
Derivatives designated as hedging instruments				6
Other operating expenses | Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income				0
Other operating expenses | Cash Flow Hedging | Interest rate derivatives
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income				$ 6