Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 3.0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Contribution Plan, Cost	2.7	$ 2.7	$ 8.1	$ 7.8
Retirement Plans
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0.8	0.9	2.6	2.7
Interest cost	1.2	1.2	3.5	3.6
Expected return on plan assets	(2.0)	(2.0)	(5.9)	(6.0)
Amortization of prior service credit	0.0	0.0	0.0	0.0
Amortization of unrecognized net loss	0.4	0.6	1.3	1.8
Settlement charge	0.4	0.7	1.5	2.7
Net periodic benefit cost	0.8	1.4	3.0	4.8
PBOP
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Service cost	0.0	0.1	0.1	0.3
Interest cost	0.4	0.5	1.2	1.5
Expected return on plan assets	(1.1)	(1.2)	(3.3)	(3.6)
Amortization of prior service credit	0.0	(0.2)	0.0	(0.7)
Amortization of unrecognized net loss	0.0	0.0	0.0	0.0
Settlement charge	0.0	0.0	0.0	0.0
Net periodic benefit cost	$ (0.7)	$ (0.8)	$ (2.0)	$ (2.5)