Income Taxes - Reconciliation of unrecognized tax benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of the beginning and ending amount of unrecognized tax benefits
Balance, January 1	$ 17.3	$ 14.5
Additions for tax positions of prior years	2.8	7.9
Additions based on tax positions related to the current year	0.1	0.5
Reductions for tax positions of prior years	(0.2)	(5.6)
Balance, December 31	20.0	17.3	$ 14.5
Income Taxes
Deferred tax assets, uncertainty in income taxes	2.0	2.1
Net amount of unrecognized tax benefits having impact on the effective tax rate for continuing operations	18.0	15.2
Interest expense in the consolidated income statements	0.5		0.2
Interest income in the consolidated income statements		0.6
Accrued penalties in the consolidated income statements	0.0	0.0	$ 0.0
Accrued interest on the consolidated balance sheets	0.7	0.2
Accrued penalties on the consolidated balance sheets	0.0	$ 0.0
Unrecognized tax benefits, decrease resulting from statute of limitations	$ 3.0