Schedule of Components of Unrealized Gain (Loss) on Securities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Change in Components of Net Unrealized Gain on Securities
Change in Net Unrealized Gain on Securities	$ 350.2	$ 710.0
Fixed Maturity Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	6,261.5	4,054.8
Change in Net Unrealized Gain on Securities	565.3	1,096.0
End of Period Balance	6,826.8	5,150.8
Other Investments
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	13.9	55.5
Change in Net Unrealized Gain on Securities	(32.3)	(14.9)
End of Period Balance	(18.4)	40.6
Deferred Acquisition Costs
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(50.8)	(41.6)
Change in Net Unrealized Gain on Securities	(5.8)	(7.3)
End of Period Balance	(56.6)	(48.9)
Reserve for Future Policy and Contract Benefits
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(6,150.3)	(4,108.5)
Change in Net Unrealized Gain on Securities	(363.6)	(831.2)
End of Period Balance	(6,513.9)	(4,939.7)
Reinsurance Recoverable
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	365.0	263.8
Change in Net Unrealized Gain on Securities	22.9	46.1
End of Period Balance	387.9	309.9
Deferred Income Tax
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(149.0)	(88.3)
Change in Net Unrealized Gain on Securities	(62.5)	(99.1)
End of Period Balance	(211.5)	(187.4)
Net Unrealized Gain on Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	290.3	135.7
Change in Net Unrealized Gain on Securities	124.0	189.6
End of Period Balance	$ 414.3	$ 325.3