REVENUE RECOGNITION - Loyalty Program Liability (Details) - Loyalty program - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Loyalty program activity
Current and noncurrent deferred revenue, beginning	$ 8,420	$ 7,882
Miles earned	1,021	999
Miles redeemed for air travel	(844)	(743)
Miles redeemed for non-air travel and other	(56)	(40)
Current and noncurrent deferred revenue, ending	$ 8,541	$ 8,098