Retirement Benefits and Trusteed Assets (Pension Plan - Assumptions used in Determining the PBO and Net Pension Costs) (Details) - Pension plan	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Projected benefit obligation
Discount rate	3.28%	4.40%	3.70%
Rate of compensation increase	4.98%	4.98%	4.98%
Net pension costs
Discount rate	4.40%	3.70%	4.25%
Rate of compensation increase	4.98%	4.98%	4.65%
Expected long-term rate of return on plan assets	7.30%	7.50%	7.50%