Pension and Postretirement Benefits (Components of net periodic benefit) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pension Benefits
Components of net periodic benefit cost
Service costs	$ 0.6	$ 0.6	$ 1.9	$ 1.8
Interest costs	0.4	0.5	1.3	1.4
Expected return on plan assets	(2.4)	(2.3)	(7.2)	(7.1)
Recognized net actuarial loss	0.3	0.3	0.9	0.9
Net periodic benefit (income) costs	(1.1)	(0.9)	$ (3.1)	$ (3.0)
Weighted average:
Discount rate			3.91%	4.13%
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	0.1	0.1	0.2	0.3
Expected return on plan assets	0.0	0.0	0.0	0.0
Recognized net actuarial loss	0.0	0.0	0.1	0.2
Net periodic benefit (income) costs	$ 0.1	$ 0.1	$ 0.3	$ 0.5
Weighted average:
Discount rate			3.63%	3.80%