Basis of Presentation and Accounting Policies - Effects of Adoption, Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Discount Rate on Future Life Policyholder Benefits	$ 276.8	$ 330.9	$ 217.6	$ 1,420.9
Other Comprehensive Loss Before Income Taxes	8.8	(81.6)	52.3	(218.0)
Other Comprehensive Income Tax (Expense) Benefit	(1.4)	17.2	(10.8)	45.8
Other Comprehensive Income (Loss), Net of Taxes	7.4	(64.4)	41.5	(172.2)
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent				(405.5)
Total Comprehensive Loss	(138.9)	(139.2)	(282.0)	(405.5)
Net Loss	$ (146.3)	(74.8)	(323.5)	(233.3)
Change in Deferred Policy Acquisition Costs			13.4	4.2
Insurance Reserves			7.9	(25.0)
Income Taxes			27.5	(62.9)
Net Cash Used in Operating Activities			$ (104.5)	(170.1)
Effect of Modified Retrospective Application Accounting Standards Update 2018-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Discount Rate on Future Life Policyholder Benefits		330.9		1,420.9
Other Comprehensive Loss Before Income Taxes		330.9		1,420.9
Other Comprehensive Income Tax (Expense) Benefit		(69.5)		(298.4)
Other Comprehensive Income (Loss), Net of Taxes		261.4		1,122.5
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent				1,134.9
Total Comprehensive Loss		262.8
Net Loss				12.4
Change in Deferred Policy Acquisition Costs				0.0
Insurance Reserves				(15.7)
Income Taxes				3.3
Net Cash Used in Operating Activities				0.0
Accounting Standards Update 2018-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Discount Rate on Future Life Policyholder Benefits		0.0		0.0
Other Comprehensive Loss Before Income Taxes		(412.5)		(1,638.9)
Other Comprehensive Income Tax (Expense) Benefit		86.7		344.2
Other Comprehensive Income (Loss), Net of Taxes		(325.8)		(1,294.7)
Other Comprehensive Income (Loss), before Tax, Portion Attributable to Parent				(1,540.4)
Total Comprehensive Loss		(402.0)
Net Loss		$ (76.2)		(245.7)
Change in Deferred Policy Acquisition Costs				4.2
Insurance Reserves				(9.3)
Income Taxes				(66.2)
Net Cash Used in Operating Activities				$ (170.1)