Benefit Plans (Weighted Average Asset Allocations) (Details)	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations	100.00%	100.00%
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations	3.30%	3.50%
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations	53.10%	53.00%
Fixed Income Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted average asset allocations	43.60%	43.50%