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Employee Benefit Plans - Weighted Average Assumptions Used in Calculating the Net Periodic Benefit Cost (Details)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Pension Benefits      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Discount rate 3.33% 4.35% 3.73%
Expected long-term rate of return on plan assets 6.00% 6.45% 6.60%
Other Postretirement Benefits      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Discount rate 3.15% 4.23% 3.55%
Expected long-term rate of return on plan assets 5.60% 6.00% 6.60%