Income Taxes (Rollforward of Uncertain Tax Positions) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Uncertain Tax Positions [Rollforward]
Beginning balance	$ 13.5	$ 9.4	$ 8.1
Additions based on tax positions related to the current year	1.5	3.7	2.7
Additions for tax positions of prior years	3.4	0.7	0.0
Reductions for tax positions of prior years	0.0	(0.3)	(1.4)
Ending balance	$ 18.4	$ 13.5	$ 9.4