Income From Investments - Net Impairment Losses Recognized in Earnings (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Investment Income [Line Items]
Net Impairment Losses Recognized in Earnings	$ (14.7)	$ (3.3)	$ (2.2)	$ (7.0)	$ (6.5)	$ (3.8)	$ (4.1)	$ (0.8)	$ (27.2)	$ (15.2)	$ (13.9)
Fixed Maturities [Member]
Net Investment Income [Line Items]
Net Impairment Losses Recognized in Earnings									(11.5)	(5.7)	(10.3)
Equity Securities [Member]
Net Investment Income [Line Items]
Net Impairment Losses Recognized in Earnings									(15.7)	(7.1)	(3.6)
Real Estate [Member]
Net Investment Income [Line Items]
Net Impairment Losses Recognized in Earnings									$ 0.0	$ (2.4)	$ 0.0