Income Taxes - Components of The Provision For Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Current income tax provision	$ 1.9	$ 0.4	$ 2.5
Deferred tax expense (benefit)	16.3	(197.2)	2.1
Total income tax provision (benefit)	$ 18.2	$ (196.8)	$ 4.6