EMPLOYEE BENEFIT PLANS - PILOT LONG-TERM DISABILITY BENEFITS (Details) - Postretirement Health Coverage [Member] - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Total liability net of a prefunded trust account	$ 25	$ 28
Prefunded trust account	$ 3	$ 3