LEASES - NARRATIVE (Details) $ in Millions	12 Months Ended
	Dec. 31, 2022 USD ($) aircraft	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)
Lessee, Lease, Description [Line Items]
Sublease Income | $	$ 15	$ 16	$ 14
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability | $	461
Operating Lease, Payments | $	354
Lessor, Operating Lease, Lease Not yet Commenced, Assumption and Judgment, Value of Underlying Asset, Amount | $	$ 213
E175 [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract	12 years
B737 MAX [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract	12 years
A321neo [Member] | Maximum [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Term of Contract	9 years
Property Subject to Operating Lease [Member] | Q400
Lessee, Lease, Description [Line Items]
Operating leases, number of leased assets (in aircraft)	6
Property Subject to Operating Lease [Member] | E175 [Member]
Lessee, Lease, Description [Line Items]
Operating leases, number of leased assets (in aircraft)	42
Property Subject to Operating Lease [Member] | B737-800
Lessee, Lease, Description [Line Items]
Operating leases, number of leased assets (in aircraft)	10
Property Subject to Operating Lease [Member] | B737 MAX [Member]
Lessee, Lease, Description [Line Items]
Operating leases, number of leased assets (in aircraft)	10
Property Subject to Operating Lease [Member] | A320 ac [Member]
Lessee, Lease, Description [Line Items]
Operating leases, number of leased assets (in aircraft)	32
Property Subject to Operating Lease [Member] | A321neo [Member]
Lessee, Lease, Description [Line Items]
Operating leases, number of leased assets (in aircraft)	10
Property Subject to Operating Lease [Member] | A319 [Member]
Lessee, Lease, Description [Line Items]
Operating leases, number of leased assets (in aircraft)	4
Property Subject to Operating Lease [Member] | A319, nonop [Member]
Lessee, Lease, Description [Line Items]
Operating leases, number of leased assets (in aircraft)	4
Property Subject to Operating Lease [Member] | A320, nonop [Member]
Lessee, Lease, Description [Line Items]
Operating leases, number of leased assets (in aircraft)	20
Property Subject to Operating Lease [Member] | Q400, nonop [Member]
Lessee, Lease, Description [Line Items]
Operating leases, number of leased assets (in aircraft)	5
Airport Facilities [Member]
Lessee, Lease, Description [Line Items]
Variable Lease, Cost | $	$ 381	377	286
Aircraft Leases [Member]
Lessee, Lease, Description [Line Items]
Variable Lease, Cost | $	10	5	1
Corporate real estate [Member]
Lessee, Lease, Description [Line Items]
Variable Lease, Cost | $	$ 27	$ 17	$ 12