Income Taxes - Components of The Provision For Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Current income tax expense	$ 0.0	$ (1.9)	$ (0.4)
Deferred tax expense (benefit)	(6.9)	(16.3)	197.2
Total income tax benefit (expense)	$ (6.9)	$ (18.2)	$ 196.8