Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Unrecognized tax benefits [Roll Forward]
Balance as of beginning of period	$ 103.8	$ 84.5
Additions based on tax positions related to current period	0.0	2.5
Additions for tax positions of prior years	0.7	21.2
Expiration of statutes of limitations	0.0	0.0
Settlements of uncertain tax positions with tax authorities	0.0	(4.4)
Balance as of end of period	$ 104.5	$ 103.8