LEASES - Maturity of Lease Liabilities (Details) $ in Millions	Dec. 31, 2019 USD ($)
Aircraft Leases [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	$ 245
Lessee, Operating Lease, Liability, Payments, Due Year Two	216
Lessee, Operating Lease, Liability, Payments, Due Year Three	190
Lessee, Operating Lease, Liability, Payments, Due Year Four	133
Lessee, Operating Lease, Liability, Payments, Due Year Five	81
Lessee, Operating Lease, Liability, Payments, Due after Year Five	331
Lessee, Operating Lease, Liability, Payments, Due	1,196
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	151
Operating Lease, Liability	1,045
CPA Aircraft [Member]
Lessee, Lease, Description [Line Items]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	79
Lessee, Operating Lease, Liability, Payments, Due Year Two	79
Lessee, Operating Lease, Liability, Payments, Due Year Three	79
Lessee, Operating Lease, Liability, Payments, Due Year Four	79
Lessee, Operating Lease, Liability, Payments, Due Year Five	79
Lessee, Operating Lease, Liability, Payments, Due after Year Five	329
Lessee, Operating Lease, Liability, Payments, Due	724
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	128
Operating Lease, Liability	596
Airport Facilities [Member]
Lessee, Lease, Description [Line Items]
Operating Leases, Future Minimum Payments, Next Rolling Twelve Months	3
Lessee, Operating Lease, Liability, Payments, Due Year Two	2
Lessee, Operating Lease, Liability, Payments, Due Year Three	2
Lessee, Operating Lease, Liability, Payments, Due Year Four	2
Lessee, Operating Lease, Liability, Payments, Due Year Five	2
Lessee, Operating Lease, Liability, Payments, Due after Year Five	11
Lessee, Operating Lease, Liability, Payments, Due	22
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	4
Operating Lease, Liability	18
Corporate real estate [Member]
Lessee, Lease, Description [Line Items]
Operating Leases, Future Minimum Payments, Next Rolling Twelve Months	8
Lessee, Operating Lease, Liability, Payments, Due Year Two	6
Lessee, Operating Lease, Liability, Payments, Due Year Three	5
Lessee, Operating Lease, Liability, Payments, Due Year Four	5
Lessee, Operating Lease, Liability, Payments, Due Year Five	5
Lessee, Operating Lease, Liability, Payments, Due after Year Five	74
Lessee, Operating Lease, Liability, Payments, Due	103
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	54
Operating Lease, Liability	$ 49