Investments (Schedule of Realized Gain (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fixed Maturities [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from Sales	$ 92.6	$ 94.2	$ 322.7	$ 402.1
Gross Gains	3.0	3.6	8.2	9.5
Gross Losses	0.5	0.3	1.9	4.5
Equity Securities [Member]
Gain (Loss) on Investments [Line Items]
Proceeds from Sales	68.2	20.7	114.5	194.1
Gross Gains	12.0		17.9	26.4
Gross Losses	$ 0.2	$ 1.2	$ 0.3	$ 2.9