REVENUE RECOGNITION - Loyalty Program Liability (Details) - Loyalty program - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Loyalty program activity
Current and noncurrent deferred revenue, beginning	$ 8,420	$ 7,882
Miles earned	3,303	3,164
Miles redeemed for air travel	(2,798)	(2,547)
Miles redeemed for non-air travel and other	(173)	(126)
Current and noncurrent deferred revenue, ending	$ 8,752	$ 8,373