Comprehensive Income - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Fuel and oil expense	$ 1,417	$ 1,564	$ 4,548	$ 4,514
Tax expense	22	44	65	202
Other operating expenses	1,079	958	3,188	2,868
Net of tax	67	$ 193	204	$ 717
Amounts reclassified from AOCI
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Net of tax	13		46
Fuel derivatives | Fuel derivatives | Amounts reclassified from AOCI
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Fuel and oil expense	15		54
Tax expense	4		13
Net of tax	11		41
Other | Fuel derivatives | Amounts reclassified from AOCI
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax expense	0		1
Other operating expenses	2		6
Net of tax	$ 2		$ 5