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Other Postretirement Employee Benefit Plans (Weighted Average Assumptions Used To Determine Benefit Obligations) (Details) - Other postretirement benefits
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]    
Discount rate 2.10% 3.10%
Medical trend rate - initial 5.50% 5.70%
Medical trend rate - grading period 17 years 18 years
Medical trend rate - ultimate 4.50% 4.50%