Retirement Plans (Pension Plan Asset Allocations) (Details) - Pension Plan	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plan actual asset allocations	100.00%	100.00%
Equity securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plan actual asset allocations	68.00%	69.00%
Debt securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plan actual asset allocations	28.00%	29.00%
Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension plan actual asset allocations	4.00%	2.00%