REVENUE RECOGNITION - Loyalty Program Liability (Details) - Loyalty program - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Loyalty Program
Current and noncurrent deferred revenue, beginning	$ 7,882	$ 7,559	$ 7,182
Miles earned	4,173	3,419	2,238
Travel miles redeemed	(3,462)	(2,898)	(1,786)
Non-travel miles redeemed	(173)	(198)	(75)
Current and noncurrent deferred revenue, ending	$ 8,420	$ 7,882	$ 7,559