Schedule of Components of Unrealized Gain (Loss) on Securities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Change in Components of Net Unrealized Gain on Securities
Change in Net Unrealized Gain on Securities	$ 176.9	$ 800.1
Fixed Maturity Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	4,664.6	3,695.7
Change in Net Unrealized Gain on Securities	261.0	1,198.8
End of Period Balance	4,925.6	4,894.5
Other Investments
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(22.7)	(33.7)
Change in Net Unrealized Gain on Securities	4.9	15.6
End of Period Balance	(17.8)	(18.1)
Deferred Acquisition Costs
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(38.9)	(29.4)
Change in Net Unrealized Gain on Securities	(2.0)	(12.6)
End of Period Balance	(40.9)	(42.0)
Reserve for Future Policy and Contract Benefits
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(4,253.2)	(3,578.4)
Change in Net Unrealized Gain on Securities	(214.1)	(888.1)
End of Period Balance	(4,467.3)	(4,466.5)
Reinsurance Recoverable
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	321.3	263.2
Change in Net Unrealized Gain on Securities	14.3	47.0
End of Period Balance	335.6	310.2
Income Tax
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(230.5)	(113.1)
Change in Net Unrealized Gain on Securities	(21.7)	(126.6)
End of Period Balance	(252.2)	(239.7)
Net Unrealized Gain on Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	440.6	204.3
Change in Net Unrealized Gain on Securities	42.4	234.1
End of Period Balance	$ 483.0	$ 438.4