REVENUE RECOGNITION - Narrative (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Revenue recognized that was previously deferred	$ 6,700	$ 3,900
Cash sales of mileage credits	$ 5,200	$ 4,100
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