Postretirement Benefits Other Than Pensions - Changes in Fair Value of Plan Assets and Changes in Accumulated Benefit Obligations (Details) - Other Postretirement Benefit Plan, Defined Benefit [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plan Assets at Beginning of Year	$ 0.0	$ 0.0
Employer Contributions	1.1	0.9
Defined Benefit Plan, Plan Assets, Contributions by Plan Participant	0.3	0.5
Plan Participants' Contributions	0.3	0.5
Benefits Paid	(1.4)	(1.4)
Fair Value of Plan Assets at End of Year	0.0	0.0	$ 0.0
Defined Benefit Plan, Benefit Obligation, Prescription Drug Subsidy Receipt	0.2	0.2
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit Obligations at Beginning of Year	14.4	15.1
Obligation from Acquisition of Infinity	3.9	0.0
Service Cost	0.2	0.1	0.1
Interest Cost	0.4	0.4	0.8
Plan Amendments			(11.0)
Actuarial (Gains) Losses	(3.0)	(0.5)
Projected Benefit Obligation at End of Year	15.0	14.4	$ 15.1
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(15.0)	(14.4)
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax	24.9	25.0
Defined Benefit Plan, Plan Assets, Benefits Paid	$ 1.4	$ 1.4