Comprehensive Income - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Fuel and oil expense	$ 1,599	$ 1,403	$ 3,130	$ 2,950
Tax expense	111	203	44	158
Other operating expenses	1,093	956	2,110	1,909
Net of tax	367	$ 683	137	$ 524
Amounts reclassified from AOCI
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Net of tax	15		33
Fuel derivative contracts | Fuel derivatives | Amounts reclassified from AOCI
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Fuel and oil expense	17		39
Tax expense	4		10
Net of tax	13		29
Other | Fuel derivatives | Amounts reclassified from AOCI
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax expense	0		0
Other operating expenses	2		4
Net of tax	$ 2		$ 4