Pensions and Postretirement Benefits (Summary of Change in Defined Benefit and Postretirement Benefit Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in plan assets
Fair value of plan assets at beginning of year	$ 128.2
Fair value of plan assets at end of year	144.4	$ 128.2
Funded (underfunded) status of the plans
Pension assets	65.0	57.0
Pension Benefits
Change in benefit obligation
Benefit obligation at beginning of year	71.2	60.5
Service costs	3.8	3.7	$ 2.4
Interest costs	2.6	2.2	1.8
Actuarial losses (gains)	7.4	(5.3)
Acquisition of CDF	0.0	14.9
Benefits and expenses paid	(5.6)	(4.8)
Benefit obligation at end of year	79.4	71.2	60.5
Change in plan assets
Fair value of plan assets at beginning of year	128.2	134.8
Actual return on plan assets	22.7	(12.1)
Company contributions	0.0	0.0
Cash transfer to fund postretirement benefit payments	(0.9)	(1.0)
Acquisition of CDF	0.0	11.3
Benefits and expenses paid	(5.6)	(4.8)
Fair value of plan assets at end of year	144.4	128.2	134.8
Funded (underfunded) status of the plans	65.0	57.0
Funded (underfunded) status of the plans
Pension assets	65.0	57.0
Other current liabilities	0.0	0.0
Other long-term liabilities	0.0	0.0
Total assets (liabilities) recognized in the consolidated balance sheets	65.0	57.0
Amounts recognized in Accumulated other comprehensive loss
Net actuarial loss	28.1	34.7
Net prior service cost (credit)	0.2	0.3
Accumulated other comprehensive loss	28.3	35.0
Postretirement Benefits
Change in benefit obligation
Benefit obligation at beginning of year	8.5	9.3
Service costs	0.0	0.0	0.0
Interest costs	0.3	0.3	0.3
Actuarial losses (gains)	0.5	0.4
Acquisition of CDF	0.0	0.0
Benefits and expenses paid	(1.3)	(1.5)
Benefit obligation at end of year	8.0	8.5	9.3
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	1.3	1.5
Cash transfer to fund postretirement benefit payments	0.0	0.0
Acquisition of CDF	0.0	0.0
Benefits and expenses paid	(1.3)	(1.5)
Fair value of plan assets at end of year	0.0	0.0	$ 0.0
Funded (underfunded) status of the plans	(8.0)	(8.5)
Funded (underfunded) status of the plans
Pension assets	0.0	0.0
Other current liabilities	0.9	0.9
Other long-term liabilities	7.1	7.6
Total assets (liabilities) recognized in the consolidated balance sheets	(8.0)	(8.5)
Amounts recognized in Accumulated other comprehensive loss
Net actuarial loss	2.6	2.4
Net prior service cost (credit)	0.0	(0.1)
Accumulated other comprehensive loss	$ 2.6	$ 2.3