Comprehensive Income (Loss) - Differences between Net Income and Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2023	Jun. 30, 2022
Condensed Statement of Income Captions [Line Items]
NET INCOME	$ 683		$ 760		$ 524	$ 482
Other, net of deferred taxes of $4 and $—	(4)		0		(4)	0
Total other comprehensive loss	(139)		(86)		(286)	417
COMPREHENSIVE INCOME	544	$ (306)	674	$ 225	238	899
Other deferred taxes	4		0		4	0
Fuel derivative contracts
Condensed Statement of Income Captions [Line Items]
Unrealized gain (loss) on derivative instruments, net of deferred taxes	(137)		(95)		(284)	403
Derivative deferred taxes	(42)		(29)		(86)	122
Interest rate derivatives
Condensed Statement of Income Captions [Line Items]
Unrealized gain (loss) on derivative instruments, net of deferred taxes	2		9		2	14
Derivative deferred taxes	$ 1		$ 3		$ 1	$ 5