REVENUE RECOGNITION - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Revenue recognized that was previously deferred	$ 3,900	$ 2,200
Cash sales of mileage credits	$ 1,700	$ 1,200
Redemption period for majority of new miles (in years)	2 years
Air traffic
Disaggregation of Revenue [Line Items]
Contract with customer, liability			$ 8,300
Contract with customer, liability, noncurrent			$ 100