Schedule of Components of Unrealized Gain (Loss) on Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Change in Components of Net Unrealized Gain on Securities
Change in Net Unrealized Gain (Loss) on Securities	$ 661.9	$ (1,720.9)	$ 1,439.3
Fixed Maturity Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Year Balance	3,695.7	6,261.5	4,054.8
Change in Net Unrealized Gain (Loss) on Securities	968.9	(2,565.8)	2,206.7
End of Year Balance	4,664.6	3,695.7	6,261.5
Other Investments
Change in Components of Net Unrealized Gain on Securities
Beginning of Year Balance	(33.7)	13.9	55.5
Change in Net Unrealized Gain (Loss) on Securities	11.0	(47.6)	(41.6)
End of Year Balance	(22.7)	(33.7)	13.9
Deferred Acquisition Costs
Change in Components of Net Unrealized Gain on Securities
Beginning of Year Balance	(29.4)	(50.8)	(41.6)
Change in Net Unrealized Gain (Loss) on Securities	(9.5)	21.4	(9.2)
End of Year Balance	(38.9)	(29.4)	(50.8)
Reserve for Future Policy and Contract Benefits
Change in Components of Net Unrealized Gain on Securities
Beginning of Year Balance	(3,578.4)	(6,150.3)	(4,108.5)
Change in Net Unrealized Gain (Loss) on Securities	(674.8)	2,571.9	(2,041.8)
End of Year Balance	(4,253.2)	(3,578.4)	(6,150.3)
Reinsurance Recoverable
Change in Components of Net Unrealized Gain on Securities
Beginning of Year Balance	263.2	365.0	263.8
Change in Net Unrealized Gain (Loss) on Securities	58.1	(101.8)	101.2
End of Year Balance	321.3	263.2	365.0
Income Tax
Change in Components of Net Unrealized Gain on Securities
Beginning of Year Balance	(113.1)	(149.0)	(88.3)
Change in Net Unrealized Gain (Loss) on Securities	(117.4)	35.9	(60.7)
End of Year Balance	(230.5)	(113.1)	(149.0)
Net Unrealized Gain on Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Year Balance	204.3	290.3	135.7
Change in Net Unrealized Gain (Loss) on Securities	236.3	(86.0)	154.6
End of Year Balance	$ 440.6	$ 204.3	$ 290.3