Retirement Benefit Plans (Weighted Average Assumptions used to Determine Net Periodic Benefit Cost) (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Expected long-term return on assets (as a percent)		5.50%
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate (as a percent)	3.07%		4.12%	3.50%
Expected long-term return on assets (as a percent)		5.75%	6.00%	6.00%
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate (as a percent)	2.82%		3.95%	3.30%
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate (as a percent)		2.50%	3.69%	3.00%
Assumed healthcare cost trend (as a percent)	6.50%	6.50%	6.50%	7.00%