Income From Investments - Net Realized Gains on Sales of Investments (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]
Realized Investment Gains									$ 55.3	$ 41.7	$ 99.5
Realized Investment Losses									(2.9)	(2.5)	(1.0)
Gain on Sale of Subsidiary									0.0	1.6	0.0
Trading Securities, Realized Gain (Loss)									(0.3)	(0.1)	0.6
Net Realized Gains (Losses) on Sales of Investments	$ 9.4	$ 5.3	$ 34.0	$ 3.4	$ 21.0	$ 8.0	$ 3.5	$ 6.6	52.1	39.1	99.1
Fixed Maturities [Member]
Net Investment Income [Line Items]
Gains on Sales									16.1	7.0	30.9
Losses on Sales									(1.1)	(0.2)	(0.4)
Equity Securities [Member]
Net Investment Income [Line Items]
Gains on Sales									39.2	33.1	21.8
Losses on Sales									(1.6)	(2.0)	(0.5)
Investee [Member]
Net Investment Income [Line Items]
Equity Method Limited Liability Investment, Gains on Sales									0.0	0.0	2.5
Real Estate Investment [Member]
Net Investment Income [Line Items]
Realized Investment Gains									0.0	0.0	44.2
Realized Investment Losses									(0.2)	(0.2)	0.0
Other Investment [Member]
Net Investment Income [Line Items]
Realized Investment Gains									0.0	0.0	0.1
Realized Investment Losses									$ 0.0	$ (0.1)	$ (0.1)