FINANCIAL DERIVATIVE INSTRUMENTS - Location and Amount Recognized in Income by Hedging Relationship (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Cash Flow Hedging
Derivative [Line Items]
Amount of gain reclassified from AOCI into income	$ 231	$ (508)
Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of gain reclassified from AOCI into income	238	(494)
Cash Flow Hedging | Interest rate derivatives
Derivative [Line Items]
Amount of gain reclassified from AOCI into income	(7)	(14)
Fuel and oil
Derivative [Line Items]
Derivatives designated as hedging instruments	(128)	(832)
Fuel and oil | Cash Flow Hedging | Fuel derivative contracts
Derivative [Line Items]
Amount of gain reclassified from AOCI into income	(128)	(832)
Fuel and oil | Cash Flow Hedging | Interest rate derivatives
Derivative [Line Items]
Amount of gain 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 reclassified from AOCI into income	0
Other operating expenses | Cash Flow Hedging | Interest rate derivatives
Derivative [Line Items]
Amount of gain reclassified from AOCI into income	$ 7
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 reclassified from AOCI into income		0
Other operating expenses | Cash Flow Hedging | Interest rate derivatives
Derivative [Line Items]
Amount of gain reclassified from AOCI into income		$ 7