Schedule of Components of Unrealized Gain (Loss) on Securities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Change in Components of Net Unrealized Gain on Securities
Change in Net Unrealized Gain on Securities	$ (1,666.7)	$ 1,245.1
Fixed Maturity Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	6,364.4	2,736.5
Change in Net Unrealized Gain on Securities	(2,103.2)	1,571.9
End of Period Balance	4,261.2	4,308.4
Deferred Acquisition Costs
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(62.7)	(27.9)
Change in Net Unrealized Gain on Securities	25.3	(14.7)
End of Period Balance	(37.4)	(42.6)
Reserve for Future Policy and Contract Benefits
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(5,803.1)	(3,220.3)
Change in Net Unrealized Gain on Securities	1,903.6	(1,230.7)
End of Period Balance	(3,899.5)	(4,451.0)
Reinsurance Recoverable
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	424.7	261.4
Change in Net Unrealized Gain on Securities	(102.0)	67.1
End of Period Balance	322.7	328.5
Income Tax
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(307.4)	(62.1)
Change in Net Unrealized Gain on Securities	55.7	(81.3)
End of Period Balance	(251.7)	(143.4)
Net Unrealized Gain (Loss) on Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	615.9	(312.4)
Change in Net Unrealized Gain on Securities	(220.6)	312.3
End of Period Balance	$ 395.3	$ (0.1)