Comprehensive Loss - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Fuel and oil expense	$ 1,531	$ 1,547
Other operating expenses	1,018	952
Tax expense	(67)	(46)
NET LOSS	(231)	$ (159)
Amounts reclassified from AOCI
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
NET LOSS	18
Fuel derivative contracts | Fuel and Interest Rate Derivatives | Amounts reclassified from AOCI
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Fuel and oil expense	22
Tax expense	6
NET LOSS	16
Other | Fuel and Interest Rate Derivatives | Amounts reclassified from AOCI
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Other operating expenses	2
Tax expense	0
NET LOSS	$ 2