Comprehensive Income (Loss) - Reclassifications (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Fuel and oil	$ 1,403	$ 1,636	$ 2,950	$ 2,640
Other (gains) losses, net	(7)	25	(21)	96
Less: Tax expense	203	276	158	178
Interest expense	65	93	130	186
Net income	683	$ 760	524	$ 482
Reclassification to earnings
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Net income	(14)		(34)
Fuel derivative contracts | Fuel and Interest Rate Derivatives | Reclassification to earnings
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Fuel and oil	(14)		(42)
Less: Tax expense	(3)		(10)
Net income	(11)		(32)
Interest rate derivatives | Fuel and Interest Rate Derivatives | Reclassification to earnings
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Less: Tax expense	1		1
Interest expense	2		3
Net income	1		2
Other Contract | Fuel and Interest Rate Derivatives | Reclassification to earnings
Reclassification Out of Accumulated Other Comprehensive Income (Loss) [Line Items]
Less: Tax expense	4		4
Net income	(4)		(4)
Other Income	$ 0		$ 0