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Retirement Plans (Weighted Average Assumptions Used To Determine Benefit Obligations) (Details)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Pension Benefits      
Compensation And Retirement Disclosure Line Items      
Benefit obligation discount rate 2.54% 3.19% 4.28%
Rate of increase in compensation levels 2.66% 2.68%  
Other  Post-retirement Benefits      
Compensation And Retirement Disclosure Line Items      
Benefit obligation discount rate 2.52% 3.18%  
Healthcare cost trend rate:      
Trend rate for next year 6.00% 6.00%  
Ultimate trend rate 5.00% 5.00%  
Year rate reaches ultimate trend rate 2024 2024