EMPLOYEE BENEFIT PLANS - Allocation of Plan Assets (Details) - Postretirement Benefit Plans	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation	100.00%	100.00%
Actual plan asset allocation	100.00%	100.00%
Equity securities
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation	21.00%	21.00%
Actual plan asset allocation	21.00%	26.00%
Debt securities
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation	74.00%	74.00%
Actual plan asset allocation	73.00%	74.00%
Other
Defined Benefit Plan, Assets, Target Allocations [Abstract]
Target allocation	5.00%	5.00%
Actual plan asset allocation	6.00%	0.00%