Pensions and Postretirement Benefits (Summary of Components of Net Periodic Benefit Cost) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits
Components of net periodic benefit cost
Service costs	$ 2.4	$ 2.4	$ 2.6
Interest costs	1.8	1.8	2.3
Expected return on plan assets	(9.7)	(9.4)	(10.2)
Amortization of prior service cost (credit)	0.0	0.0	0.0
Recognized net actuarial loss	1.2	1.1	0.3
Benefit (income) costs	(4.3)	(4.1)	(5.0)
Other changes in plan assets and benefit obligations recognized in accumulated other comprehensive (income) loss
AOCI at beginning of year	26.1	25.5	15.7
Net (loss) gain arising during the year	(1.1)	1.7	10.1
Recognition of prior service credit	0.0	0.0	0.0
Recognition of actuarial loss	(8.2)	(1.1)	(0.3)
Total recognized in accumulated other comprehensive loss at end of year	16.8	26.1	25.5
Postretirement Benefits
Components of net periodic benefit cost
Service costs	0.0	0.0	0.0
Interest costs	0.3	0.3	0.6
Expected return on plan assets	0.0	0.0	0.0
Amortization of prior service cost (credit)	(0.1)	(0.1)	(0.1)
Recognized net actuarial loss	0.1	0.1	0.5
Benefit (income) costs	0.3	0.3	1.0
Other changes in plan assets and benefit obligations recognized in accumulated other comprehensive (income) loss
AOCI at beginning of year	1.5	4.1	7.2
Net (loss) gain arising during the year	0.5	(2.6)	(2.7)
Recognition of prior service credit	0.1	0.1	0.1
Recognition of actuarial loss	(0.1)	(0.1)	(0.5)
Total recognized in accumulated other comprehensive loss at end of year	$ 2.0	$ 1.5	$ 4.1