BENEFIT PLANS - Weighted-Average Assumptions used to Determine Net Periodic Benefit Cost (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Weighted-average assumptions used to determine net periodic benefit cost at December 31,
Discount rate	3.73%	4.23%	4.86%
Expected return on plan assets	7.14%	7.14%	7.14%
Rate of compensation increase	4.88%	4.88%	4.80%
Other Benefits
Weighted-average assumptions used to determine net periodic benefit cost at December 31,
Discount rate	3.60%	3.98%	4.39%
Expected return on plan assets	7.25%	7.25%	7.25%