Income Taxes - Summary of Components of Company's Income Tax Provision (Benefit) from Continuing Operations (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2015
Current
U.S. federal	$ 7.9	$ (30.6)	$ 3.2	$ 33.0
State and local	1.2	1.0	3.2	3.4
Current income tax provision (benefit)	9.1	(29.6)	6.4	36.4
Deferred
U.S. federal	(6.2)	116.0	2.8	(41.2)
State and local	(0.9)	9.7	2.0	5.1
Deferred income tax provision (benefit)	(7.1)	125.7	4.8	(36.1)
Income tax provision	$ 2.0	$ 96.1	$ 11.2	$ 0.3