Pension and Postretirement Benefits (Components of net periodic benefit) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Pension Benefits
Components of net periodic benefit cost
Service costs	$ 1.0	$ 0.6
Interest costs	0.5	0.5
Expected return on plan assets	(2.9)	(2.4)
Recognized net actuarial loss	0.1	0.2
Net periodic benefit (income) costs	$ (1.3)	$ (1.1)
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
Interest costs	0.1	0.1
Expected return on plan assets	0.0	0.0
Recognized net actuarial loss	0.0	0.0
Net periodic benefit (income) costs	$ 0.1	$ 0.1
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%