Long-Duration Insurance Contracts - Balances of and Changes in the LFPB (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits	$ 1,635.7	$ 1,622.8
Whole Life
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	229.1
Beginning period (including reserves)			$ 223.2
Beginning balance at original discount rate	263.2
Beginning balance at original discount rate (including reserves)		247.1
Change in cash flow assumptions		0.0	13.8
Actual variances from expected experience		(0.6)	3.2
Adjusted balance		262.6	264.1
Issuances	2.5	12.6
Interest accruals	2.0	7.6
Net premiums collected	(5.1)	(21.1)
Ending balance at original discount rate	262.0	263.2
Effect of changes in discount rate assumptions	(31.0)	(34.1)
Ending balance	231.0	229.1
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	504.3
Beginning balance (including reserves)		522.0
Beginning balance at original discount rate	618.2	617.4
Beginning balance at original discount rate (including reserves)		592.1
Changes in cash flow assumptions		0.0	13.7
Actual variances from expected experience		(1.1)	3.4
Adjusted balance		616.3	609.2
Issuances	2.4	12.6
Interest accruals	5.2	19.8
Benefit payments	(5.7)	(24.2)
Ending balance at original discount rate	618.2	617.4
Effect of changes in discount rate assumptions	(107.5)	(113.1)
Ending balance	510.7	504.3
Net liability for future policy benefits	279.7	275.2
Less: Reinsurance recoverable	(60.7)	(60.2)
Net liability for future policy benefits, after reinsurance recoverable	219.0	215.0
Impact of flooring on net liability for future policy benefits	0.0	0.0
Net liability for future policy benefits	219.0	215.0
Term Life
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	245.9
Beginning period (including reserves)			240.0
Beginning balance at original discount rate	271.2
Beginning balance at original discount rate (including reserves)		256.6
Change in cash flow assumptions		0.0	4.6
Actual variances from expected experience		(2.5)	(0.5)
Adjusted balance		268.7	260.7
Issuances	5.8	25.2
Interest accruals	2.8	10.7
Net premiums collected	(6.3)	(25.4)
Ending balance at original discount rate	271.0	271.2
Effect of changes in discount rate assumptions	(21.4)	(25.3)
Ending balance	249.6	245.9
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	377.8
Beginning balance (including reserves)		370.1
Beginning balance at original discount rate	437.3	433.2
Beginning balance at original discount rate (including reserves)		405.4
Changes in cash flow assumptions		0.0	5.6
Actual variances from expected experience		(3.2)	(1.0)
Adjusted balance		430.0	410.0
Issuances	5.9	25.5
Interest accruals	4.3	16.1
Benefit payments	(2.9)	(18.4)
Ending balance at original discount rate	437.3	433.2
Effect of changes in discount rate assumptions	(49.4)	(55.4)
Ending balance	387.9	377.8
Net liability for future policy benefits	138.4	131.8
Less: Reinsurance recoverable	(20.7)	(19.3)
Net liability for future policy benefits, after reinsurance recoverable	117.7	112.5
Impact of flooring on net liability for future policy benefits	0.2	0.0
Net liability for future policy benefits	117.9	112.5
Experience life
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	66.6
Beginning period (including reserves)			71.7
Beginning balance at original discount rate	65.4
Beginning balance at original discount rate (including reserves)		67.0
Change in cash flow assumptions		0.0	1.5
Actual variances from expected experience		(1.6)	0.0
Adjusted balance		63.8	68.5
Issuances	0.0	0.0
Interest accruals	0.9	3.7
Net premiums collected	(1.6)	(6.8)
Ending balance at original discount rate	63.1	65.4
Effect of changes in discount rate assumptions	1.8	1.2
Ending balance	64.9	66.6
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	813.2
Beginning balance (including reserves)		883.0
Beginning balance at original discount rate	776.3	782.8
Beginning balance at original discount rate (including reserves)		797.5
Changes in cash flow assumptions		0.0	2.2
Actual variances from expected experience		(2.2)	0.2
Adjusted balance		780.6	799.9
Issuances	0.0	0.0
Interest accruals	11.5	46.7
Benefit payments	(15.8)	(63.8)
Ending balance at original discount rate	776.3	782.8
Effect of changes in discount rate assumptions	38.5	30.4
Ending balance	814.8	813.2
Net liability for future policy benefits	749.9	746.6
Less: Reinsurance recoverable	(0.9)	(0.9)
Net liability for future policy benefits, after reinsurance recoverable	749.0	745.7
Impact of flooring on net liability for future policy benefits	0.0	0.0
Net liability for future policy benefits	749.0	745.7
Limited-Pay Whole Life
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	34.2
Beginning period (including reserves)			32.2
Beginning balance at original discount rate	36.8
Beginning balance at original discount rate (including reserves)		33.9
Change in cash flow assumptions		0.0	2.2
Actual variances from expected experience		(0.3)	0.0
Adjusted balance		36.5	36.1
Issuances	0.5	4.0
Interest accruals	0.4	1.4
Net premiums collected	(1.2)	(4.7)
Ending balance at original discount rate	36.2	36.8
Effect of changes in discount rate assumptions	(2.2)	(2.6)
Ending balance	34.0	34.2
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	86.2
Beginning balance (including reserves)		89.6
Beginning balance at original discount rate	115.1	114.3
Beginning balance at original discount rate (including reserves)		105.6
Changes in cash flow assumptions		0.0	2.4
Actual variances from expected experience		(0.4)	0.0
Adjusted balance		113.9	108.0
Issuances	0.5	4.0
Interest accruals	1.1	4.2
Benefit payments	(0.4)	(1.9)
Ending balance at original discount rate	115.1	114.3
Effect of changes in discount rate assumptions	(27.4)	(28.1)
Ending balance	87.7	86.2
Net liability for future policy benefits	53.7	52.1
Less: Reinsurance recoverable	(1.4)	(1.4)
Net liability for future policy benefits, after reinsurance recoverable	52.3	50.7
Impact of flooring on net liability for future policy benefits	0.0	0.0
Net liability for future policy benefits	52.3	50.7
Supplemental health
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	179.9
Beginning period (including reserves)			182.0
Beginning balance at original discount rate	214.6
Beginning balance at original discount rate (including reserves)		213.4
Change in cash flow assumptions		0.0	(5.2)
Actual variances from expected experience		(1.5)	2.9
Adjusted balance		213.1	211.1
Issuances	6.1	20.9
Interest accruals	1.7	6.8
Net premiums collected	(6.3)	(24.2)
Ending balance at original discount rate	214.6	214.6
Effect of changes in discount rate assumptions	(32.0)	(34.7)
Ending balance	182.6	179.9
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	383.4
Beginning balance (including reserves)		427.6
Beginning balance at original discount rate	480.1	482.8
Beginning balance at original discount rate (including reserves)		517.9
Changes in cash flow assumptions		0.0	(6.5)
Actual variances from expected experience		(2.1)	2.5
Adjusted balance		480.7	513.9
Issuances	6.1	20.9
Interest accruals	3.5	14.4
Benefit payments	(10.2)	(66.4)
Ending balance at original discount rate	480.1	482.8
Effect of changes in discount rate assumptions	(94.5)	(99.4)
Ending balance	385.6	383.4
Net liability for future policy benefits	203.0	203.5
Less: Reinsurance recoverable	(4.3)	(4.7)
Net liability for future policy benefits, after reinsurance recoverable	198.7	198.8
Impact of flooring on net liability for future policy benefits	0.0	0.0
Net liability for future policy benefits	198.7	198.8
Cancer
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits	72.1	72.2
Accident
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits	18.7	18.8
Disability
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits	21.8	21.4
Other
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits	86.1	86.4
SPIA (life contingent)
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	0.0
Beginning period (including reserves)			0.0
Beginning balance at original discount rate	0.0
Beginning balance at original discount rate (including reserves)		0.0
Change in cash flow assumptions		0.0	0.0
Actual variances from expected experience		0.0	0.0
Adjusted balance		0.0	0.0
Issuances	0.6	2.8
Interest accruals	0.0	0.0
Net premiums collected	(0.6)	(2.8)
Ending balance at original discount rate	0.0	0.0
Effect of changes in discount rate assumptions	0.0	0.0
Ending balance	0.0	0.0
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	97.3
Beginning balance (including reserves)		104.2
Beginning balance at original discount rate	106.0	107.3
Beginning balance at original discount rate (including reserves)		111.4
Changes in cash flow assumptions		0.0	0.0
Actual variances from expected experience		(0.2)	0.2
Adjusted balance		107.1	$ 111.6
Issuances	0.6	2.8
Interest accruals	1.0	4.3
Benefit payments	(2.7)	(11.4)
Ending balance at original discount rate	106.0	107.3
Effect of changes in discount rate assumptions	(8.8)	(10.0)
Ending balance	97.2	97.3
Net liability for future policy benefits	97.2	97.3
Less: Reinsurance recoverable	(3.6)	(3.5)
Net liability for future policy benefits, after reinsurance recoverable	93.6	93.8
Impact of flooring on net liability for future policy benefits	0.0	0.0
Net liability for future policy benefits	$ 93.6	$ 93.8