Basis of Presentation and Significant Accounting Policies - Schedule of Changes in LFPB due to Adoption of ASU 2018-12 (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Jan. 01, 2022	Dec. 31, 2021	Dec. 31, 2020
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for future policy benefits	$ 1,772.4	$ 1,718.0
Previously Reported
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for future policy benefits
Whole Life
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for future policy benefits	292.8	278.4		$ 317.7	$ 330.6
Effect of changes in cash flow assumptions		0.0	$ 5.2		2.8
Less: Reinsurance recoverable	(65.0)	(63.1)		(0.5)	(0.1)
Less: Change in discount rate assumptions					(0.2)
Net liability for future policy benefits at March 31, 2023	228.1	216.4		317.2	330.3
Whole Life | Previously Reported
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for future policy benefits					218.7
Whole Life | Change in discount rate assumptions
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Effect of changes in cash flow assumptions					111.5
Whole Life | Change in cash flow assumptions, effect of net premiums exceeding gross premiums
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Effect of changes in cash flow assumptions					0.4
Term Life
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for future policy benefits	121.2	112.2		117.6	120.5
Effect of changes in cash flow assumptions		0.0	21.5		(4.8)
Less: Reinsurance recoverable	(16.6)	(15.3)		(5.5)	(5.4)
Less: Change in discount rate assumptions					(0.9)
Net liability for future policy benefits at March 31, 2023	104.6	97.1		112.1	114.2
Term Life | Previously Reported
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for future policy benefits					93.2
Term Life | Change in discount rate assumptions
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Effect of changes in cash flow assumptions					27.3
Term Life | Change in cash flow assumptions, effect of net premiums exceeding gross premiums
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Effect of changes in cash flow assumptions					0.0
Experience Life
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for future policy benefits	822.8	799.3		1,098.1	1,191.3
Effect of changes in cash flow assumptions		0.0	11.0		(3.6)
Less: Reinsurance recoverable	(0.8)	(0.8)		(1.1)	(1.3)
Less: Change in discount rate assumptions					(0.7)
Net liability for future policy benefits at March 31, 2023	822.0	798.5		1,097.0	1,189.3
Experience Life | Previously Reported
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for future policy benefits					758.3
Experience Life | Change in discount rate assumptions
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Effect of changes in cash flow assumptions					433.0
Experience Life | Change in cash flow assumptions, effect of net premiums exceeding gross premiums
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Effect of changes in cash flow assumptions					0.0
Limited Pay Whole Life
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for future policy benefits	53.3	49.6		73.2	69.5
Effect of changes in cash flow assumptions		0.0	2.0		0.0
Less: Reinsurance recoverable	(0.1)	0.0		(0.2)	(0.1)
Less: Change in discount rate assumptions					(0.1)
Net liability for future policy benefits at March 31, 2023	53.2	49.6		73.0	69.3
Limited Pay Whole Life | Previously Reported
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for future policy benefits					51.3
Limited Pay Whole Life | Change in discount rate assumptions
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Effect of changes in cash flow assumptions					18.2
Limited Pay Whole Life | Change in cash flow assumptions, effect of net premiums exceeding gross premiums
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Effect of changes in cash flow assumptions					0.0
Supplemental Health
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for future policy benefits					415.5
Less: Reinsurance recoverable					0.0
Less: Change in discount rate assumptions					0.0
Net liability for future policy benefits at March 31, 2023					415.5
Supplemental Health | Previously Reported
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for future policy benefits					392.5
Supplemental Health | Change in discount rate assumptions
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Effect of changes in cash flow assumptions					23.0
Supplemental Health | Change in cash flow assumptions, effect of net premiums exceeding gross premiums
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Effect of changes in cash flow assumptions					0.0
Cancer
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at March 31, 2023	101.7	101.8		140.8	163.5
Accident
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at March 31, 2023	22.2	21.8		28.7	31.2
Disability
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at March 31, 2023	23.7	23.1		29.3	32.0
Other
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at March 31, 2023	114.0	114.3		160.3	188.8
SPIA (life contingent)
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for future policy benefits	105.9	103.3		124.7	136.5
Effect of changes in cash flow assumptions		0.0	$ 0.0		0.0
Less: Reinsurance recoverable	(3.5)	(3.2)		0.0	0.0
Less: Change in discount rate assumptions					0.0
Net liability for future policy benefits at March 31, 2023	$ 102.4	$ 100.1		$ 124.7	136.5
SPIA (life contingent) | Previously Reported
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for future policy benefits					115.9
SPIA (life contingent) | Change in discount rate assumptions
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Effect of changes in cash flow assumptions					20.6
SPIA (life contingent) | Change in cash flow assumptions, effect of net premiums exceeding gross premiums
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Effect of changes in cash flow assumptions					$ 0.0