Benefit Plans (Amounts Recognized in Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net actuarial loss (gain)	$ 74.5	$ 86.0
Prior service credit	(0.8)	(2.3)
Total	73.7	83.7
Defined Benefit Plan, Excess of Net Periodic Benefit Cost Over Other Comprehensive Income	0.3	18.9	$ 20.3
Other Postretirement Benefits Plan [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net actuarial loss (gain)	(10.4)	(11.9)
Prior service credit	(2.4)	(3.0)
Total	(12.8)	(14.9)
Defined Benefit Plan, Excess of Net Periodic Benefit Cost Over Other Comprehensive Income	$ (0.8)	$ (2.1)	$ 0.1