Benefit Plans (Amounts Recognized in Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net actuarial loss (gain)	$ 86.0	$ 79.9
Transition obligation	0.0	0.1
Prior service credit	(2.3)	(5.7)
Total	83.7	74.3
Other Retirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Net actuarial loss (gain)	(11.9)	(13.2)
Transition obligation	0.0	0.0
Prior service credit	(3.0)	0.0
Total	$ (14.9)	$ (13.2)