Pensions and Postretirement Benefits (Summary of Change in Defined Benefit and Postretirement Benefit Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in plan assets
Fair value of plan assets at beginning of year	$ 120.2
Fair value of plan assets at end of year	134.8	$ 120.2
Funded (underfunded) status of the plans
Pension assets	74.3	61.7
Pension Benefits
Change in benefit obligation
Benefit obligation at beginning of year	58.5	58.4
Service costs	2.4	2.4	$ 2.6
Interest costs	1.8	1.8	2.3
Actuarial losses (gains)	2.4	0.5
Benefits and expenses paid	(4.6)	(4.6)
Benefit obligation at end of year	60.5	58.5	58.4
Change in plan assets
Fair value of plan assets at beginning of year	120.2	117.3
Actual return on plan assets	20.2	8.3
Company contributions	0.0	0.0
Cash transfer to fund postretirement benefit payments	(1.0)	(0.8)
Benefits and expenses paid	(4.6)	(4.6)
Fair value of plan assets at end of year	134.8	120.2	117.3
Funded (underfunded) status of the plans	74.3	61.7
Funded (underfunded) status of the plans
Pension assets	74.3	61.7
Other current liabilities	0.0	0.0
Other long-term liabilities	0.0	0.0
Total assets (liabilities) recognized in the consolidated balance sheets	74.3	61.7
Amounts recognized in Accumulated other comprehensive loss
Net actuarial loss	16.5	25.8
Net prior service cost (credit)	0.3	0.3
Accumulated other comprehensive loss	16.8	26.1
Postretirement Benefits
Change in benefit obligation
Benefit obligation at beginning of year	10.0	13.5
Service costs	0.0	0.0	0.0
Interest costs	0.3	0.3	0.6
Actuarial losses (gains)	0.5	(2.6)
Benefits and expenses paid	(1.5)	(1.2)
Benefit obligation at end of year	9.3	10.0	13.5
Change in plan assets
Fair value of plan assets at beginning of year	0.0	0.0
Actual return on plan assets	0.0	0.0
Company contributions	1.5	1.2
Cash transfer to fund postretirement benefit payments	0.0	0.0
Benefits and expenses paid	(1.5)	(1.2)
Fair value of plan assets at end of year	0.0	0.0	$ 0.0
Funded (underfunded) status of the plans	(9.3)	(10.0)
Funded (underfunded) status of the plans
Pension assets	0.0	0.0
Other current liabilities	1.1	1.2
Other long-term liabilities	8.2	8.8
Total assets (liabilities) recognized in the consolidated balance sheets	(9.3)	(10.0)
Amounts recognized in Accumulated other comprehensive loss
Net actuarial loss	2.1	1.7
Net prior service cost (credit)	(0.1)	(0.2)
Accumulated other comprehensive loss	$ 2.0	$ 1.5