LEASES - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) lease aircraft airport
Lessee, Lease, Description [Line Items]
Leases that have not yet commenced | $	$ 151
Minimum
Lessee, Lease, Description [Line Items]
Leases that have not yet commenced, term of contract	4 years
Maximum
Lessee, Lease, Description [Line Items]
Leases that have not yet commenced, term of contract	19 years
Aircraft
Lessee, Lease, Description [Line Items]
Number of leases	225
Number of finance leases	111
Number of operating leases	114
Lease component of purchase agreements, number of aircraft | aircraft	116
Aircraft | Minimum
Lessee, Lease, Description [Line Items]
Remaining term of operating leases	5 months
Remaining term of finance leases	5 months
Aircraft | Maximum
Lessee, Lease, Description [Line Items]
Remaining term of operating leases	12 years
Remaining term of finance leases	12 years
Airport Facilities
Lessee, Lease, Description [Line Items]
Number of airports with facility space under lease | airport	300
Airport Facilities | Minimum
Lessee, Lease, Description [Line Items]
Remaining term of operating leases	1 month
Airport Facilities | Maximum
Lessee, Lease, Description [Line Items]
Remaining term of operating leases	29 years
Other Ground Property and Equipment | Minimum
Lessee, Lease, Description [Line Items]
Remaining term of operating leases	1 month
Remaining term of finance leases	1 month
Other Ground Property and Equipment | Maximum
Lessee, Lease, Description [Line Items]
Remaining term of operating leases	6 years
Remaining term of finance leases	6 years