Income Taxes (Components of Income Tax) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current expense
Federal and other	$ 41.1	$ 0.7	$ 2.1
Foreign	30.5	22.9	16.0
Total current income tax expense	71.6	23.6	18.1
Deferred expense (benefit)
Federal and other	(47.4)	3.5	22.8
Foreign	2.2	2.5	4.6
Total deferred income tax (benefit) expense	(45.2)	6.0	27.4
Income tax expense	$ 26.4	$ 29.6	$ 45.5