EMPLOYEE BENEFITS - Schedule of Assumptions used To Calculate Pension and SERP and PBOP (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)	7.00%
Expected Long-Term Rate of Return (in percentage)	7.00%
Compensation/Progression Rate (in percentage)	4.00%
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Expected Long-Term Rate of Return (in percentage)		8.25%	8.25%
Compensation/Progression Rate (in percentage)		3.50%	3.50%
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Expected Long-Term Rate of Return (in percentage)		8.25%	8.25%
Minimum | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)	3.85%	3.20%	3.27%
Expected Long-Term Rate of Return (in percentage)	8.25%
Compensation/Progression Rate (in percentage)	3.50%
Minimum | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)	3.28%	3.48%	2.88%
Expected Long-Term Rate of Return (in percentage)	8.25%
Maximum | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)	4.62%	3.90%	4.89%
Maximum | Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Discount Rate (in percentage)	3.94%	4.64%	4.09%