Schedule of Components of Unrealized Gain (Loss) on Securities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Change in Components of Net Unrealized Gain on Securities
Change in Net Unrealized Gain on Securities	$ 2,507.7	$ 1,047.7	$ 841.0	$ 2,292.8
Fixed Maturity Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	4,261.2	4,308.4	6,364.4	2,736.5
Change in Net Unrealized Gain on Securities	3,161.6	1,327.0	1,058.4	2,898.9
End of Period Balance	7,422.8	5,635.4	7,422.8	5,635.4
Deferred Acquisition Costs
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(37.4)	(42.6)	(62.7)	(27.9)
Change in Net Unrealized Gain on Securities	(32.0)	(14.4)	(6.7)	(29.1)
End of Period Balance	(69.4)	(57.0)	(69.4)	(57.0)
Reserve for Future Policy and Contract Benefits
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(3,899.5)	(4,451.0)	(5,803.1)	(3,220.3)
Change in Net Unrealized Gain on Securities	(2,560.3)	(1,004.7)	(656.7)	(2,235.4)
End of Period Balance	(6,459.8)	(5,455.7)	(6,459.8)	(5,455.7)
Reinsurance Recoverable
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	322.7	328.5	424.7	261.4
Change in Net Unrealized Gain on Securities	141.8	57.2	39.8	124.3
End of Period Balance	464.5	385.7	464.5	385.7
Income Tax
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	(251.7)	(143.4)	(307.4)	(62.1)
Change in Net Unrealized Gain on Securities	(143.3)	(78.1)	(87.6)	(159.4)
End of Period Balance	(395.0)	(221.5)	(395.0)	(221.5)
Net Unrealized Gain on Securities
Change in Components of Net Unrealized Gain on Securities
Beginning of Period Balance	395.3	(0.1)	615.9	(312.4)
Change in Net Unrealized Gain on Securities	567.8	287.0	347.2	599.3
End of Period Balance	$ 963.1	$ 286.9	$ 963.1	$ 286.9