Income Taxes - Components of The Provision For Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Current income tax expense	$ (1.1)	$ 0.0	$ (1.9)
Deferred tax expense	(142.1)	(6.9)	(16.3)
Total income tax expense	$ (143.2)	$ (6.9)	$ (18.2)