Schedule of Components of Unrealized Gain (Loss) on Securities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Change in Components of Net Unrealized Gain on Securities
Change in Net Unrealized Gain on Securities	$ 1,245.1	$ (1,042.1)
Fixed Maturity Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	2,736.5	5,665.2
Change in Net Unrealized Gain on Securities	1,571.9	(1,317.0)
End of Period Balance	4,308.4	4,348.2
Deferred Acquisition Costs
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(27.9)	(51.4)
Change in Net Unrealized Gain on Securities	(14.7)	10.2
End of Period Balance	(42.6)	(41.2)
Reserve for Future Policy and Contract Benefits
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(3,220.3)	(5,094.7)
Change in Net Unrealized Gain on Securities	(1,230.7)	1,064.6
End of Period Balance	(4,451.0)	(4,030.1)
Reinsurance Recoverable
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	261.4	375.8
Change in Net Unrealized Gain on Securities	67.1	(54.8)
End of Period Balance	328.5	321.0
Income Tax
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(62.1)	(304.6)
Change in Net Unrealized Gain on Securities	(81.3)	62.8
End of Period Balance	(143.4)	(241.8)
Net Unrealized Gain on Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(312.4)	590.3
Change in Net Unrealized Gain on Securities	312.3	(234.2)
End of Period Balance	$ (0.1)	$ 356.1