LEASES - Lease Cost (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) Rate
Lessee, Lease, Description [Line Items]
Operating Lease, Expense	$ 668
Sublease Income	13
Lease, Cost	655
Aircraft Leases [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 246
Operating Lease, Weighted Average Discount Rate, Percent | Rate	4.00%
Operating Lease, Weighted Average Remaining Lease Term	7 years
CPA Aircraft [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 79
Operating Lease, Weighted Average Discount Rate, Percent | Rate	4.30%
Operating Lease, Weighted Average Remaining Lease Term	9 years 2 months 12 days
Airport Facilities [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 324
Operating Lease, Weighted Average Discount Rate, Percent | Rate	4.10%
Operating Lease, Weighted Average Remaining Lease Term	10 years
Corporate real estate [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 19
Operating Lease, Weighted Average Discount Rate, Percent | Rate	4.20%
Operating Lease, Weighted Average Remaining Lease Term	34 years 10 months 24 days