EMPLOYEE BENEFIT PLANS - Assumptions Used in Calculations (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Assumptions used to determine benefit obligations at December 31:
Discount rate	2.26%	3.06%	4.11%
Assumptions used to determine net periodic benefit cost for years ended December 31:
Discount rate	3.06%	4.11%	3.48%
Expected long-term return on plan assets	5.72%	5.72%	7.17%
Postretirement
Assumptions used to determine benefit obligations at December 31:
Discount rate	2.42%	3.16%	4.18%
Assumptions used to determine net periodic benefit cost for years ended December 31:
Discount rate	3.16%	4.18%	3.56%
Expected long-term return on plan assets	0.00%	0.00%	0.00%