EMPLOYEE BENEFIT PLANS - Net Periodic Benefit Cost: Weighted Average Assumptions (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Employee benefit plans
Discount rate	3.20%	4.20%
Long-term rate of return on plan assets	6.25%	6.50%
Rate of compensation increases	3.25%	3.25%
Cost of living adjustment	2.50%	2.50%
Pension Benefits | SERP
Employee benefit plans
Rate of compensation increases	3.75%	3.75%
Other Benefits
Employee benefit plans
Discount rate	3.25%	4.25%
Long-term rate of return on plan assets	5.50%	5.50%
Rate of compensation increases	0.00%	0.00%
Other Benefits | SERP
Employee benefit plans
Rate of compensation increases	0.00%	0.00%