Schedule of Components of Unrealized Gain (Loss) on Securities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Change in Components of Net Unrealized Gain on Securities
Change in Net Unrealized Gain on Securities	$ 481.4	$ 800.4	$ 1,322.4	$ 3,093.2
Fixed Maturity Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	7,422.8	5,635.4	6,364.4	2,736.5
Change in Net Unrealized Gain on Securities	608.0	1,009.9	1,666.4	3,908.8
End of Period Balance	8,030.8	6,645.3	8,030.8	6,645.3
Deferred Acquisition Costs
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(69.4)	(57.0)	(62.7)	(27.9)
Change in Net Unrealized Gain on Securities	(5.8)	(7.7)	(12.5)	(36.8)
End of Period Balance	(75.2)	(64.7)	(75.2)	(64.7)
Reserve for Future Policy and Contract Benefits
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(6,459.8)	(5,455.7)	(5,803.1)	(3,220.3)
Change in Net Unrealized Gain on Securities	(511.5)	(878.5)	(1,168.2)	(3,113.9)
End of Period Balance	(6,971.3)	(6,334.2)	(6,971.3)	(6,334.2)
Reinsurance Recoverable
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	464.5	385.7	424.7	261.4
Change in Net Unrealized Gain on Securities	87.4	48.4	127.2	172.7
End of Period Balance	551.9	434.1	551.9	434.1
Income Tax
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(395.0)	(221.5)	(307.4)	(62.1)
Change in Net Unrealized Gain on Securities	(36.7)	(36.9)	(124.3)	(196.3)
End of Period Balance	(431.7)	(258.4)	(431.7)	(258.4)
Net Unrealized Gain on Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	963.1	286.9	615.9	(312.4)
Change in Net Unrealized Gain on Securities	141.4	135.2	488.6	734.5
End of Period Balance	$ 1,104.5	$ 422.1	$ 1,104.5	$ 422.1