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Pension Plan and Other Postretirement Benefits - Weighted-average Assumptions Used to Determine Net Periodic Benefit Cost (Details)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Discount Rate 3.47% 4.50% 3.90%
Long-Term Rate of Return on Plan Assets 6.88% 7.25% 7.50%
Pension Plan | Participants to Age 39      
Defined Benefit Plan Disclosure [Line Items]      
Rate of Increase in Future Compensation Level: 4.50% 4.50% 4.50%
Pension Plan | Participants Age 40 to Age 49      
Defined Benefit Plan Disclosure [Line Items]      
Rate of Increase in Future Compensation Level: 3.50% 3.50% 3.50%
Pension Plan | Participants Age 50 and Older      
Defined Benefit Plan Disclosure [Line Items]      
Rate of Increase in Future Compensation Level: 2.75% 2.75% 2.75%
Executive Survivor and Supplemental Retirement Plan      
Defined Benefit Plan Disclosure [Line Items]      
Discount Rate 3.36% 4.46% 3.85%
Rate of Increase in Future Compensation Level: 3.50% 3.40% 2.92%
Other Postretirement Benefits Plan      
Defined Benefit Plan Disclosure [Line Items]      
Discount Rate 3.43% 4.44% 3.81%