Income Taxes Income Taxes - Reconciliation of Unrecognized Tax Benefits for the Period (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Unrecognized tax benefits	$ 19.7	$ 18.2	$ 17.9	$ 28.7
Unrecognized tax benefits, increase resulting from prior period tax positions	0.9	0.9	0.7
Unrecognized tax benefits, increase resulting from current period tax positions	0.6	0.0	0.8
Unrecognized tax benefits, decrease resulting from settlements with taxing authorities	0.0	(0.1)	0.0
Unrecognized tax benefits, decrease resulting from prior period tax positions	$ 0.0	$ (0.5)	$ (12.3)