Income Taxes Uncertain tax positions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2012
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Unrecognized Tax Benefits	$ 40.3	$ 39.8	$ 4.1	$ 42.2
Tax positions taken in current year	0.6	26.9	0.0
Tax positions taken in prior years	1.2	10.4	0.9
Tax positions taken in current year	0.0	0.0	0.0
Tax positions taken in prior years	(1.3)	0.0	(0.5)
Settlements during the year	0.0	0.0	(34.7)
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations	0.0	(1.6)	$ (3.8)
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	39.9	39.8
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	0.7	3.0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	$ 3.7	$ 3.0