Long-Duration Insurance Contracts - Balances of and Changes in the LFPB (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Jan. 01, 2022	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
Whole Life
Present Value of Expected Net Premiums
Beginning balance	215.1	183.0	$ 176.5
Beginning balance at original discount rate	245.9	157.6	143.5
Change in cash flow assumptions		0.0		$ 5.2	$ 2.4
Actual variances from expected experience		0.8		7.2	8.8
Adjusted balance		246.7		251.7	154.7
Issuances	2.8	12.5	13.3
Interest accruals	1.8	6.7	6.2
Net premiums collected	(4.7)	(25.0)	(16.6)
Ending balance at original discount rate	246.6	245.9	157.6
Effect of changes in discount rate assumptions	(24.4)	(30.8)	25.4
Ending balance	222.2	215.1	183.0
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	493.6	500.7	507.1
Beginning balance at original discount rate	585.4	581.9	386.3	566.1	362.5
Changes in cash flow assumptions		0.0		5.2	2.8
Actual variances from expected experience		0.8		7.7	8.7
Adjusted balance		582.7		579.0	374.0
Issuances	2.9	12.4	13.3
Interest accruals	4.7	18.0	17.1
Benefit payments	(4.9)	(27.5)	(18.1)
Ending balance at original discount rate	585.4	581.9	386.3
Effect of changes in discount rate assumptions	(70.3)	(88.3)	114.4
Ending balance	515.1	493.6	500.7
Liability for future policy benefits	292.8	278.4	317.7		330.6
Less: Reinsurance recoverable	(65.0)	(63.1)	(0.5)		(0.1)
Net liability for future policy benefits, after reinsurance recoverable	227.8	215.3
Impact of flooring on net liability for future policy benefits	0.3	1.1
Net liability for future policy benefits at March 31, 2023	228.1	216.4	317.2		330.3
Term Life
Present Value of Expected Net Premiums
Beginning balance	234.7	253.1	244.1
Beginning balance at original discount rate	265.4	221.1	200.8
Change in cash flow assumptions		0.0		18.7	(4.5)
Actual variances from expected experience		(1.5)		(4.2)	6.9
Adjusted balance		263.9		249.9	203.2
Issuances	6.5	28.0	29.8
Interest accruals	2.5	9.0	7.9
Net premiums collected	(6.9)	(21.5)	(19.8)
Ending balance at original discount rate	266.0	265.4	221.1
Effect of changes in discount rate assumptions	(22.2)	(30.7)	32.0
Ending balance	243.8	234.7	253.1
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	347.0	370.6	364.7
Beginning balance at original discount rate	405.2	401.0	319.5	360.0	294.0
Changes in cash flow assumptions		0.0		21.5	(4.8)
Actual variances from expected experience		(1.5)		(4.7)	7.2
Adjusted balance		399.5		376.8	296.4
Issuances	6.6	28.3	29.8
Interest accruals	4.0	14.4	12.0
Benefit payments	(4.9)	(18.5)	(18.7)
Ending balance at original discount rate	405.2	401.0	319.5
Effect of changes in discount rate assumptions	(40.2)	(54.0)	51.1
Ending balance	365.0	347.0	370.6
Liability for future policy benefits	121.2	112.2	117.6		120.5
Less: Reinsurance recoverable	(16.6)	(15.3)	(5.5)		(5.4)
Net liability for future policy benefits, after reinsurance recoverable	104.6	96.9
Impact of flooring on net liability for future policy benefits	0.0	0.2
Net liability for future policy benefits at March 31, 2023	104.6	97.1	112.1		114.2
Experience Life
Present Value of Expected Net Premiums
Beginning balance	68.3	74.6	78.0
Beginning balance at original discount rate	65.5	55.8	55.2
Change in cash flow assumptions		0.0		9.1	(3.3)
Actual variances from expected experience		0.2		3.0	6.3
Adjusted balance		65.7		68.0	58.2
Issuances	0.0	0.0	0.0
Interest accruals	1.0	3.3	3.2
Net premiums collected	(1.7)	(5.8)	(5.6)
Ending balance at original discount rate	65.0	65.5	55.8
Effect of changes in discount rate assumptions	4.8	2.8	18.8
Ending balance	69.8	68.3	74.6
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	867.5	1,172.7	1,269.3
Beginning balance at original discount rate	801.5	805.2	802.5	802.6	813.5
Changes in cash flow assumptions		0.0		11.0	(3.6)
Actual variances from expected experience		0.4		3.6	6.6
Adjusted balance		805.6		817.2	816.5
Issuances	0.0	0.0	0.0
Interest accruals	11.9	47.4	47.9
Benefit payments	(16.0)	(59.4)	(61.9)
Ending balance at original discount rate	801.5	805.2	802.5
Effect of changes in discount rate assumptions	91.0	62.3	370.2
Ending balance	892.5	867.5	1,172.7
Liability for future policy benefits	822.8	799.3	1,098.1		1,191.3
Less: Reinsurance recoverable	(0.8)	(0.8)	(1.1)		(1.3)
Net liability for future policy benefits, after reinsurance recoverable	822.0	798.5
Impact of flooring on net liability for future policy benefits	0.0	0.0
Net liability for future policy benefits at March 31, 2023	822.0	798.5	1,097.0		1,189.3
Limited Pay Whole Life
Present Value of Expected Net Premiums
Beginning balance	29.7	29.7	25.4
Beginning balance at original discount rate	32.4	27.2	22.0
Change in cash flow assumptions		0.0		2.0	0.0
Actual variances from expected experience		0.5		1.6	1.0
Adjusted balance		32.9		30.8	23.0
Issuances	1.0	6.3	10.2
Interest accruals	0.3	1.1	0.8
Net premiums collected	(1.1)	(5.8)	(6.8)
Ending balance at original discount rate	33.1	32.4	27.2
Effect of changes in discount rate assumptions	(1.9)	(2.7)	2.5
Ending balance	31.2	29.7	29.7
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	79.4	102.9	95.0
Beginning balance at original discount rate	100.3	98.6	86.6	86.6	73.4
Changes in cash flow assumptions		0.0		2.0	0.0
Actual variances from expected experience		0.6		1.4	1.1
Adjusted balance		99.2		90.0	74.5
Issuances	1.0	6.4	10.2
Interest accruals	0.9	3.4	2.9
Benefit payments	(0.8)	(1.2)	(1.0)
Ending balance at original discount rate	100.3	98.6	86.6
Effect of changes in discount rate assumptions	(15.9)	(19.2)	16.3
Ending balance	84.4	79.4	102.9
Liability for future policy benefits	53.3	49.6	73.2		69.5
Less: Reinsurance recoverable	(0.1)	0.0	(0.2)		(0.1)
Net liability for future policy benefits, after reinsurance recoverable	53.2	49.6
Impact of flooring on net liability for future policy benefits	0.0	0.0
Net liability for future policy benefits at March 31, 2023	53.2	49.6	73.0		69.3
Supplemental health
Present Value of Expected Net Premiums
Beginning balance	167.4	221.5	233.0
Beginning balance at original discount rate	205.1	217.5	218.2
Change in cash flow assumptions		0.0		12.2	(1.8)
Actual variances from expected experience		(1.4)		(25.3)	6.3
Adjusted balance		203.7		210.0	222.7
Issuances	5.3	12.0	13.0
Interest accruals	1.5	5.9	5.9
Net premiums collected	(5.4)	(22.8)	(24.1)
Ending balance at original discount rate	205.1	205.1	217.5
Effect of changes in discount rate assumptions	(32.6)	(37.7)	4.0
Ending balance	172.5	167.4	221.5
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	431.7	580.6	626.9
Beginning balance at original discount rate	530.6	537.1	572.6	584.2	589.1
Changes in cash flow assumptions		0.0		13.8	(3.0)
Actual variances from expected experience		(1.7)		(30.0)	6.2
Adjusted balance		535.4		568.0	592.3
Issuances	5.3	12.0	13.0
Interest accruals	3.6	15.0	15.7
Benefit payments	(13.7)	(57.9)	(48.4)
Ending balance at original discount rate	530.6	537.1	572.6
Effect of changes in discount rate assumptions	(92.9)	(105.4)	8.0
Ending balance	437.7	431.7	580.6
Liability for future policy benefits	265.3	264.4	359.1
Less: Reinsurance recoverable	(3.7)	(3.4)	0.0
Net liability for future policy benefits, after reinsurance recoverable	261.6	261.0
Impact of flooring on net liability for future policy benefits	0.0	0.0
Net liability for future policy benefits at March 31, 2023	261.6	261.0	359.1
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)
Present Value of Expected Net Premiums
Beginning balance	0.0	0.0	0.0
Beginning balance at original discount rate	0.0	0.0	0.0
Change in cash flow assumptions		0.0		0.0	0.0
Actual variances from expected experience		0.0		0.0	0.0
Adjusted balance		0.0		0.0	0.0
Issuances	2.0	5.3	3.7
Interest accruals	0.0	0.0	0.0
Net premiums collected	(2.0)	(5.3)	(3.7)
Ending balance at original discount rate	0.0	0.0	0.0
Effect of changes in discount rate assumptions	0.0	0.0	0.0
Ending balance	0.0	0.0	0.0
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	103.3	124.7	136.5
Beginning balance at original discount rate	113.3	113.4	111.6	115.7	115.9
Changes in cash flow assumptions		0.0		0.0	0.0
Actual variances from expected experience		(0.5)		0.4	(0.4)
Adjusted balance		112.9		$ 116.1	115.5
Issuances	2.4	5.3	3.7
Interest accruals	1.1	4.3	4.5
Benefit payments	(3.1)	(12.3)	(12.1)
Ending balance at original discount rate	113.3	113.4	111.6
Effect of changes in discount rate assumptions	(7.4)	(10.1)	13.1
Ending balance	105.9	103.3	124.7
Liability for future policy benefits	105.9	103.3	124.7		136.5
Less: Reinsurance recoverable	(3.5)	(3.2)	0.0		0.0
Net liability for future policy benefits, after reinsurance recoverable	102.4	100.1
Impact of flooring on net liability for future policy benefits	0.0	0.0
Net liability for future policy benefits at March 31, 2023	$ 102.4	$ 100.1	$ 124.7		$ 136.5