LEASES - Lease Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Lessee, Lease, Description [Line Items]
Operating Lease, Expense	$ 690	$ 708	$ 654
Sublease Income	15	15	16
Lease, Cost	675	693	638
Aircraft Leases [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 100	191	174
Operating Lease, Weighted Average Discount Rate, Percent	5.50%
Operating Lease, Weighted Average Remaining Lease Term	9 years 3 months 18 days
CPA Aircraft [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 108	100	80
Operating Lease, Weighted Average Discount Rate, Percent	7.00%
Operating Lease, Weighted Average Remaining Lease Term	7 years 9 months 18 days
Airport Facilities [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 451	384	379
Operating Lease, Weighted Average Discount Rate, Percent	5.30%
Operating Lease, Weighted Average Remaining Lease Term	6 years 8 months 12 days
Corporate real estate [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 31	$ 33	$ 21
Operating Lease, Weighted Average Discount Rate, Percent	5.40%
Operating Lease, Weighted Average Remaining Lease Term	26 years 7 months 6 days