Retirement Benefit Plans (Assumptions Used in Accounting for Defined Benefit Plans) (Details) - Pension Plan	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on assets for net periodic benefit cost	7.50%	7.50%	7.75%
Minimum
Defined Benefit Plan Disclosure [Line Items]
Weighted average discount rates for pension benefit obligation	3.40%	3.75%	3.90%
Weighted average discount rates for net periodic benefit cost	3.40%	3.90%	3.65%
Maximum
Defined Benefit Plan Disclosure [Line Items]
Weighted average discount rates for pension benefit obligation	3.55%	4.00%	4.20%
Weighted average discount rates for net periodic benefit cost	4.00%	4.20%	3.95%