Financial Derivative Instruments - Location and Amount Recognized in Income by Hedging Relationship (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Cash Flow Hedging
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	$ (658)	$ (93)
Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	(654)	(84)
Cash Flow Hedging | Interest rate derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	(4)	(9)
Fuel and oil
Derivative [Line Items]
Derivatives designated as hedging instruments	(203)	16
Fuel and oil | Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	(203)	16
Fuel and oil | Cash Flow Hedging | Interest rate derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	0	0
Other (gains)/losses, net
Derivative [Line Items]
Derivatives designated as hedging instruments	0	6
Other (gains)/losses, net | Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	0	6
Other (gains)/losses, net | Cash Flow Hedging | Interest rate derivative contracts
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
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 derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income	$ 2
Interest expense
Derivative [Line Items]
Derivatives designated as hedging instruments		1
Interest expense | Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income		0
Interest expense | Cash Flow Hedging | Interest rate derivative contracts
Derivative [Line Items]
Amount of (gain) loss reclassified from AOCI into income		$ 1