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PENSION AND POSTRETIREMENT BENEFIT PLANS - Assumptions (Details)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Pension Benefits    
Benefit Obligation Assumptions:    
Discount rate 3.16% 4.22%
Rate of compensation increase 4.00% 4.00%
Net Periodic Benefit Cost Assumptions:    
Discount rate 4.22% 3.53%
Assumed long-term rate of return on assets 6.50% 6.50%
Rate of compensation increase 4.00% 4.00%
Postretirement Benefits    
Benefit Obligation Assumptions:    
Discount rate 3.48% 4.57%
Rate of compensation increase 0.00% 0.00%
Net Periodic Benefit Cost Assumptions:    
Discount rate 4.57% 3.87%
Assumed long-term rate of return on assets 0.00% 0.00%
Rate of compensation increase 0.00% 0.00%
Assumed health care cost trend rates    
U.S. Consumer Price Index (CPI) increase 1.86% 1.78%
Union employees | Postretirement Benefits    
Assumed health care cost trend rates    
Annual decrease in healthcare cost in 2020 0.25%  
Projected healthcare cost rate in 2019 6.50%  
Projected healthcare cost rate in 2028 4.50%  
Projected ultimate health care cost trend rates after 2028 4.50%