LEASES - Narrative (Details)	3 Months Ended		9 Months Ended	12 Months Ended
	Mar. 31, 2023 USD ($) aircraft	Dec. 31, 2022 USD ($) aircraft	Dec. 31, 2023 USD ($) aircraft	Dec. 31, 2023 USD ($) aircraft	Dec. 31, 2022 USD ($) aircraft	Dec. 31, 2021 USD ($)	Dec. 05, 2022 aircraft
Lessee, Lease, Description [Line Items]
Capital expenditures				$ 3,520,000,000	$ 3,924,000,000	$ 505,000,000
Payments of long-term debt and finance lease obligations				85,000,000	2,437,000,000	$ 612,000,000
Total lease obligations		$ 189,000,000	$ 104,000,000	$ 104,000,000	$ 189,000,000
Airport-Related
Lessee, Lease, Description [Line Items]
Term of lease contract (in years)			37 years	37 years
Boeing 737-700 | Aircraft
Lessee, Lease, Description [Line Items]
Number of aircrafts to be purchased | aircraft			4	4
Number of aircrafts purchased | aircraft	8	31			31		39
Capital expenditures	$ 88,000,000	$ 365,000,000	$ 44,000,000
Payments of long-term debt and finance lease obligations	50,000,000	191,000,000		$ 3,000,000
Total lease obligations	$ 38,000,000	$ 174,000,000	$ 41,000,000	$ 41,000,000	$ 174,000,000
Number of leased aircrafts | aircraft			24	24
Gain (loss) on sale of aircrafts				$ 0
Minimum | Aircraft
Lessee, Lease, Description [Line Items]
Renewal term (in years)				3 months
Minimum | Other
Lessee, Lease, Description [Line Items]
Renewal term (in years)				6 months
Minimum | Airport-Related
Lessee, Lease, Description [Line Items]
Renewal term (in years)			1 year	1 year
Maximum | Aircraft
Lessee, Lease, Description [Line Items]
Term of contract (in years)				10 years
Renewal term (in years)				3 years
Maximum | Other
Lessee, Lease, Description [Line Items]
Term of contract (in years)				3 years
Renewal term (in years)				1 year
Maximum | Airport-Related
Lessee, Lease, Description [Line Items]
Renewal term (in years)			11 years	11 years