Retirement Plans (Schedule Of Assumptions Used) (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - used at year end to value obligation (in hundredths)	2.60%	3.40%	4.30%
Discount rate - used at beginning of year to compute annual cost (in hundredths)	3.40%	4.30%	3.70%
Expected long-term rate of return on plan assets (in hundredths)	7.50%	7.50%	7.50%
Rate of increase in compensation levels (in hundredths)	2.00%	2.00%	2.00%
Postretirement Benefits Other Than Pensions (OPEB) [Member] | Maximum [Member]
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - used at year end to value obligation (in hundredths)	2.80%	3.50%	4.40%
Discount rate - used at beginning of year to compute annual cost (in hundredths)	3.50%	4.40%	3.80%
Postretirement Benefits Other Than Pensions (OPEB) [Member] | Minimum [Member]
Defined Benefit Plan, Assumptions Used in Calculations [Abstract]
Discount rate - used at year end to value obligation (in hundredths)	2.60%	3.40%	4.30%
Discount rate - used at beginning of year to compute annual cost (in hundredths)	3.40%	4.30%	3.70%