REVENUE RECOGNITION - Narrative (Details) - USD ($) $ in Billions	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023
Revenue from Contract with Customer [Abstract]
Revenue recognized that was previously deferred	$ 3.9	$ 3.9
Cash sales of mileage credits	$ 1.8	$ 1.7
Redemption period for majority of new miles (in years)	2 years

Amount of revenue recognized that was previously included in balance of obligation to transfer good or service to customer for which consideration from customer has been received or is due.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 606
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479806/606-10-50-8

Name:	us-gaap_ContractWithCustomerLiabilityRevenueRecognized
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration