Income Taxes - Reconciliation of unrecognized tax benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of the beginning and ending amount of unrecognized tax benefits
Balance of unrecognized tax benefits, January 1	$ 20.0	$ 17.3
Additions for tax positions of prior years	1.9	2.8
Additions based on tax positions related to the current year	0.2	0.1
Reductions for tax positions of prior years	(4.2)	(0.2)
Balance of unrecognized tax benefits, December 31	17.9	20.0	$ 17.3
Income Taxes
Deferred tax assets, uncertainty in income taxes	2.0	2.0
Net amount of unrecognized tax benefits having impact on the effective tax rate for continuing operations	15.9	18.0
Interest expense in the consolidated income statements	0.1	0.5	0.6
Penalties in the consolidated income statements	0.0	0.0	$ 0.0
Accrued interest on the consolidated balance sheets	0.8	0.7
Accrued penalties on the consolidated balance sheets	0.0	$ 0.0
Unrecognized tax benefits, decrease resulting from statute of limitations	$ 11.4