Retirement Plans (Summary of Net Pension and Supplemental Executive Retirement Plan Expense Recognized) (Details) - USD ($) $ in Millions	3 Months Ended		8 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 10, 2016	Sep. 10, 2016	Sep. 30, 2017
Compensation and Retirement Disclosure [Abstract]
Service cost pertaining to benefits earned during the period	$ 1.8	$ 1.5	$ 4.5	$ 5.4
Interest cost on projected benefit obligations	4.5	4.5	13.3	13.3
Expected return on pension assets	(5.0)	(4.6)	(13.9)	(14.8)
Net amortization loss	2.4	1.1	3.4	7.3
Net pension expense	$ 3.7	$ 2.5	$ 7.3	$ 11.2