Pension and Other Post-Retirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016
Accumulative other comprehensive loss:
After-tax amount recognized in accumulated other comprehensive loss	$ 83.0		$ 83.0		$ 84.4	$ 85.8	$ 87.1
Defined Benefit Pension [Member]
Accumulative other comprehensive loss:
Defined Benefit Plan, Interest Cost	3.8	$ 3.9	11.5	$ 11.8
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	5.9	6.5	17.9	19.5
Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement	0.0	5.7	0.1	5.7
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	1.7	7.0	5.5	9.5
Unrecognized prior service credit	0.0	(0.2)	0.0	(0.7)
Unrecognized net actuarial loss (gain)	2.2	2.6	6.9	7.7
Other Postretirement Benefits Plan [Member]
Accumulative other comprehensive loss:
Defined Benefit Plan, Interest Cost	0.2	0.2	0.7	0.7
Defined Benefit Plan, Expected Return (Loss) on Plan Assets	0.0	0.0	0.0	0.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	0.2	0.2	0.5	0.5
Unrecognized prior service credit	0.0	(0.1)	(0.1)	(0.2)
Unrecognized net actuarial loss (gain)	$ 0.0	$ 0.0	$ (0.2)	$ (0.2)