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Benefit Plans - Actuarial Calculation Assumptions (Details)
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost, discount rate     3.52%
Net periodic benefit cost, expected return on plan assets     7.00%
Net periodic benefit cost, rate of compensation increase 4.00% 4.00% 4.00%
Benefit obligations, rate of compensation increase 4.00% 4.00%  
Other Postretirement Benefits Plan      
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost, discount rate     3.45%
Net periodic benefit cost, expected return on plan assets     7.00%
Maximum | Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost, discount rate 3.23% 4.16%  
Net periodic benefit cost, expected return on plan assets 6.75% 7.25%  
Benefit obligations, discount rate 2.48% 3.23%  
Maximum | Other Postretirement Benefits Plan      
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost, discount rate 3.18% 4.09%  
Net periodic benefit cost, expected return on plan assets 6.50% 7.00%  
Benefit obligations, discount rate 2.41% 3.18%  
Minimum | Pension Plan      
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost, discount rate 3.05% 3.04%  
Net periodic benefit cost, expected return on plan assets 6.50% 7.00%  
Benefit obligations, discount rate 2.29% 3.05%  
Minimum | Other Postretirement Benefits Plan      
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost, discount rate 2.59% 2.52%  
Net periodic benefit cost, expected return on plan assets 4.20% 4.00%  
Benefit obligations, discount rate 2.18% 2.59%