Postretirement Benefits Other Than Pensions - Changes in Fair Value of Plan Assets and Changes in Accumulated Benefit Obligations (Details) - USD ($) $ in Millions			12 Months Ended
	Aug. 22, 2019	Jul. 13, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Employer Contributions	$ 55.3	$ 5.1
Other Postretirement Benefit Plan, Defined Benefit
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair Value of Plans’ Assets at Beginning of Year			$ 0.0	$ 0.0
Employer Contributions			1.1	1.1
Plan Participants’ Contributions			0.3	0.3
Benefits Paid			(1.4)	(1.4)
Fair Value of Plan Assets at End of Year			0.0	0.0	$ 0.0
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Accumulated Postretirement Benefit Obligation at Beginning of Year			15.0	14.4
Obligation from Acquisition of Infinity			0.0	3.9
Service Cost			0.2	0.2	0.1
Interest Cost			0.4	0.4	0.4
Plan Participants’ Contributions			0.3	0.3
Benefits Paid			(1.4)	(1.4)
Medicare Part D Subsidy Received			0.0	0.2
Actuarial (Gains) Losses			(1.7)	(3.0)
Projected Benefit Obligation at End of Year			12.8	15.0	$ 14.4
Funded Status—Plan Assets in Excess (Deficit) of Projected Benefit Obligation			(12.8)	(15.0)
Unamortized Actuarial Gain Reported in AOCI at End of Year			$ 23.8	$ 24.9