Investments - Net Realized Gains on Sales of Investments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fixed Maturities [Member]
Net Investment Income [Line Items]
Realized Gains	$ 3.5	$ 4.3	$ 4.9	$ 11.4
Realized Losses	(0.2)	0.0	(0.4)	(0.3)
Equity Securities [Member]
Net Investment Income [Line Items]
Realized Gains	18.3	0.5	27.2	0.5
Realized Losses	$ 0.0	$ (0.1)	$ 0.0	$ (0.1)