Retirement Plans (Schedule Of Assumptions Used To Determine Benefit Obligations And Net Periodic Benefit Cost) (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits [Member]
Assumptions to determine benefit obligations:
Discount rate	3.14%	4.09%	3.51%
Rate of compensation increase	2.50%	2.50%	2.50%
Assumptions to determine net periodic benefit cost:
Discount rate - service cost	3.74%	3.77%	4.06%
Discount rate - interest cost	3.36%	3.14%	2.91%
Rate of compensation increase	2.50%	2.50%	4.50%
Expected return on plan assets	5.75%	5.75%	5.75%
Postretirement Benefits [Member]
Assumptions to determine benefit obligations:
Discount rate	2.81%	4.01%	3.25%
Assumptions to determine net periodic benefit cost:
Discount rate - service cost	3.99%	4.13%	4.22%
Discount rate - interest cost	3.21%	2.67%	2.39%