Retirement Benefit Plans (Percentage and Target Allocations) (Details)	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Plan Assets	100.00%	100.00%
Cash And Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets	1.00%	3.00%
Cash And Equivalents [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	0.00%	0.00%
Cash And Equivalents [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	5.00%	5.00%
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets	46.00%	41.00%
Fixed Income Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	35.00%	25.00%
Fixed Income Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	63.00%	65.00%
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets	48.00%	51.00%
Equity Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	35.00%	30.00%
Equity Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	51.00%	60.00%
Real Assets Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan Assets	5.00%	5.00%
Real Assets Fund [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	0.00%	0.00%
Real Assets Fund [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	12.00%	10.00%