Pension and Postretirement Benefits (Components of net periodic benefit) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Pension Benefits
Components of net periodic benefit cost
Service costs	$ 1.0	$ 0.7	$ 2.0	$ 1.3
Interest costs	0.6	0.4	1.1	0.9
Expected return on plan assets	(2.9)	(2.4)	(5.8)	(4.8)
Recognized net actuarial loss	0.1	0.3	0.2	0.6
Net periodic benefit (income) costs	(1.2)	(1.0)	$ (2.5)	$ (2.0)
Weighted average:
Discount rate for PBO			3.52%	3.91%
Discount rate for interest cost			3.10%	3.20%
Discount rate for service cost			3.57%	3.98%
Expected return on plan assets			8.25%	8.25%
Postretirement Benefits
Components of net periodic benefit cost
Service costs	0.0	0.0	$ 0.0	$ 0.0
Interest costs	0.0	0.0	0.1	0.1
Expected return on plan assets	0.0	0.0	0.0	0.0
Recognized net actuarial loss	0.0	0.1	0.0	0.1
Net periodic benefit (income) costs	$ 0.0	$ 0.1	$ 0.1	$ 0.2
Weighted average:
Discount rate for PBO			3.32%	3.63%
Discount rate for interest cost			2.89%	2.92%
Discount rate for service cost			3.70%	4.12%