Income Taxes - Classification of Net Deferred Income Tax Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Long-term deferred income tax assets	$ 670.2	$ 563.8
Long-term deferred income tax liabilities	(84.8)	(86.6)
Net deferred income tax asset	$ 585.4	$ 477.2