Long-Duration Insurance Contracts - Balances of and Changes in the LFPB (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for Future Policy Benefit, before Reinsurance	$ 1,622.8	$ 1,761.8
Whole Life
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	223.2	215.1
Beginning period (including reserves)				$ 260.7
Beginning balance at original discount rate	247.1	245.9
Beginning balance at original discount rate (including reserves)			$ 239.3
Change in cash flow assumptions		13.8	0.0	5.2
Actual variances from expected experience		3.2	3.8	7.2
Adjusted balance		264.1	249.7	251.7
Issuances	12.6	10.8	12.5
Interest accruals	7.6	7.2	6.7
Net premiums collected	(21.1)	(20.6)	(25.0)
Ending balance at original discount rate	263.2	247.1	245.9
Effect of changes in discount rate assumptions	(34.1)	(23.9)	(30.8)
Ending balance	229.1	223.2	215.1
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	522.0	493.6
Beginning balance (including reserves)			660.4
Beginning balance at original discount rate	617.4	592.1	581.9
Beginning balance at original discount rate (including reserves)			566.1
Changes in cash flow assumptions		13.7	(0.6)	5.2
Actual variances from expected experience		3.4	4.0	7.7
Adjusted balance		609.2	585.3	579.0
Issuances	12.6	10.7	12.4
Interest accruals	19.8	19.0	18.0
Benefit payments	(24.2)	(22.9)	(27.5)
Ending balance at original discount rate	617.4	592.1	581.9
Effect of changes in discount rate assumptions	(113.1)	(70.1)	(88.3)
Ending balance	504.3	522.0	493.6
Liability for Future Policy Benefit, before Reinsurance	275.2	298.8	278.4
Less: Reinsurance recoverable	(60.2)	(64.3)	(63.1)
Net liability for future policy benefits, after reinsurance recoverable	215.0	234.5	215.3
Impact of flooring on net liability for future policy benefits	0.0	0.0	1.1
Net liability for future policy benefits at September 30, 2023	215.0	234.5	216.4
Term Life
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	240.0	234.7
Beginning period (including reserves)				264.4
Beginning balance at original discount rate	256.6	265.4
Beginning balance at original discount rate (including reserves)			235.4
Change in cash flow assumptions		4.6	(16.8)	18.7
Actual variances from expected experience		(0.5)	(2.7)	(4.2)
Adjusted balance		260.7	245.9	249.9
Issuances	25.2	25.2	28.0
Interest accruals	10.7	10.3	9.0
Net premiums collected	(25.4)	(24.8)	(21.5)
Ending balance at original discount rate	271.2	256.6	265.4
Effect of changes in discount rate assumptions	(25.3)	(16.6)	(30.7)
Ending balance	245.9	240.0	234.7
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	370.1	347.0
Beginning balance (including reserves)			411.5
Beginning balance at original discount rate	433.2	405.4	401.0
Beginning balance at original discount rate (including reserves)			360.0
Changes in cash flow assumptions		5.6	(16.7)	21.5
Actual variances from expected experience		(1.0)	1.3	(4.7)
Adjusted balance		410.0	385.6	376.8
Issuances	25.5	25.8	28.3
Interest accruals	16.1	15.2	14.4
Benefit payments	(18.4)	(21.2)	(18.5)
Ending balance at original discount rate	433.2	405.4	401.0
Effect of changes in discount rate assumptions	(55.4)	(35.3)	(54.0)
Ending balance	377.8	370.1	347.0
Liability for Future Policy Benefit, before Reinsurance	131.8	130.2	112.2
Less: Reinsurance recoverable	(19.3)	(19.1)	(15.3)
Net liability for future policy benefits, after reinsurance recoverable	112.5	111.1	96.9
Impact of flooring on net liability for future policy benefits	0.0	0.0	0.2
Net liability for future policy benefits at September 30, 2023	112.5	111.1	97.1
Experience Life
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	71.7	68.3
Beginning period (including reserves)				74.6
Beginning balance at original discount rate	67.0	65.5
Beginning balance at original discount rate (including reserves)			55.9
Change in cash flow assumptions		1.5	3.7	9.1
Actual variances from expected experience		0.0	0.7	3.0
Adjusted balance		68.5	69.9	68.0
Issuances	0.0	0.0	0.0
Interest accruals	3.7	3.7	3.3
Net premiums collected	(6.8)	(6.6)	(5.8)
Ending balance at original discount rate	65.4	67.0	65.5
Effect of changes in discount rate assumptions	1.2	4.7	2.8
Ending balance	66.6	71.7	68.3
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	883.0	867.5
Beginning balance (including reserves)			1,172.7
Beginning balance at original discount rate	782.8	797.5	805.2
Beginning balance at original discount rate (including reserves)			802.6
Changes in cash flow assumptions		2.2	5.0	11.0
Actual variances from expected experience		0.2	1.1	3.6
Adjusted balance		799.9	811.3	817.2
Issuances	0.0	0.0	0.0
Interest accruals	46.7	47.4	47.4
Benefit payments	(63.8)	(61.2)	(59.4)
Ending balance at original discount rate	782.8	797.5	805.2
Effect of changes in discount rate assumptions	30.4	85.5	62.3
Ending balance	813.2	883.0	867.5
Liability for Future Policy Benefit, before Reinsurance	746.6	811.3	799.3
Less: Reinsurance recoverable	(0.9)	(1.0)	(0.8)
Net liability for future policy benefits, after reinsurance recoverable	745.7	810.3	798.5
Impact of flooring on net liability for future policy benefits	0.0	0.0	0.0
Net liability for future policy benefits at September 30, 2023	745.7	810.3	798.5
Limited-Pay Whole Life
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	32.2	29.7
Beginning period (including reserves)				29.7
Beginning balance at original discount rate	33.9	32.4
Beginning balance at original discount rate (including reserves)			27.2
Change in cash flow assumptions		2.2	(0.2)	2.0
Actual variances from expected experience		0.0	1.0	1.6
Adjusted balance		36.1	33.2	30.8
Issuances	4.0	4.3	6.3
Interest accruals	1.4	1.2	1.1
Net premiums collected	(4.7)	(4.8)	(5.8)
Ending balance at original discount rate	36.8	33.9	32.4
Effect of changes in discount rate assumptions	(2.6)	(1.7)	(2.7)
Ending balance	34.2	32.2	29.7
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	89.6	79.4
Beginning balance (including reserves)			102.9
Beginning balance at original discount rate	114.3	105.6	98.6
Beginning balance at original discount rate (including reserves)			86.6
Changes in cash flow assumptions		2.4	(0.2)	2.0
Actual variances from expected experience		0.0	1.0	1.4
Adjusted balance		108.0	99.4	90.0
Issuances	4.0	4.3	6.4
Interest accruals	4.2	3.9	3.4
Benefit payments	(1.9)	(2.0)	(1.2)
Ending balance at original discount rate	114.3	105.6	98.6
Effect of changes in discount rate assumptions	(28.1)	(16.0)	(19.2)
Ending balance	86.2	89.6	79.4
Liability for Future Policy Benefit, before Reinsurance	52.1	57.4	49.6
Less: Reinsurance recoverable	(1.4)	(1.2)	0.0
Net liability for future policy benefits, after reinsurance recoverable	50.7	56.2	49.6
Impact of flooring on net liability for future policy benefits	0.0	0.0	0.0
Net liability for future policy benefits at September 30, 2023	50.7	56.2	49.6
Supplemental Health
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	182.0	167.4
Beginning period (including reserves)				226.7
Beginning balance at original discount rate	213.4	205.1
Beginning balance at original discount rate (including reserves)			223.1
Change in cash flow assumptions		(5.2)	6.5	12.2
Actual variances from expected experience		2.9	(1.6)	(25.3)
Adjusted balance		211.1	210.0	210.0
Issuances	20.9	19.4	12.0
Interest accruals	6.8	6.0	5.9
Net premiums collected	(24.2)	(22.0)	(22.8)
Ending balance at original discount rate	214.6	213.4	205.1
Effect of changes in discount rate assumptions	(34.7)	(31.4)	(37.7)
Ending balance	179.9	182.0	167.4
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	427.6	431.7
Beginning balance (including reserves)			590.6
Beginning balance at original discount rate	482.8	517.9	537.1
Beginning balance at original discount rate (including reserves)			584.2
Changes in cash flow assumptions		(6.5)	8.9	13.8
Actual variances from expected experience		2.5	(2.4)	(30.0)
Adjusted balance		513.9	543.6	568.0
Issuances	20.9	19.4	12.0
Interest accruals	14.4	14.4	15.0
Benefit payments	(66.4)	(59.5)	(57.9)
Ending balance at original discount rate	482.8	517.9	537.1
Effect of changes in discount rate assumptions	(99.4)	(90.3)	(105.4)
Ending balance	383.4	427.6	431.7
Liability for Future Policy Benefit, before Reinsurance	203.5	245.6	264.4
Less: Reinsurance recoverable	(4.7)	(4.0)	(3.4)
Net liability for future policy benefits, after reinsurance recoverable	198.8	241.6	261.0
Impact of flooring on net liability for future policy benefits	0.0	0.0	0.0
Net liability for future policy benefits at September 30, 2023	198.8	241.6	261.0
Cancer
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at September 30, 2023	72.2	92.7	101.8
Accident
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at September 30, 2023	18.8	21.4	21.8
Disability
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at September 30, 2023	21.4	23.5	23.1
Other
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at September 30, 2023	86.4	104.0	114.3
SPIA (life contingent)
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	0.0	0.0
Beginning period (including reserves)				0.0
Beginning balance at original discount rate	0.0	0.0
Beginning balance at original discount rate (including reserves)			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	2.8	5.6	5.3
Interest accruals	0.0	0.0	0.0
Net premiums collected	(2.8)	(5.6)	(5.3)
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	104.2	103.3
Beginning balance (including reserves)			129.1
Beginning balance at original discount rate	107.3	111.4	113.4
Beginning balance at original discount rate (including reserves)			115.7
Changes in cash flow assumptions		0.0	0.0	0.0
Actual variances from expected experience		0.2	(0.8)	0.4
Adjusted balance		111.6	112.6	$ 116.1
Issuances	2.8	6.3	5.3
Interest accruals	4.3	4.4	4.3
Benefit payments	(11.4)	(11.9)	(12.3)
Ending balance at original discount rate	107.3	111.4	113.4
Effect of changes in discount rate assumptions	(10.0)	(7.2)	(10.1)
Ending balance	97.3	104.2	103.3
Liability for Future Policy Benefit, before Reinsurance	97.3	104.2	103.3
Less: Reinsurance recoverable	(3.5)	(3.6)	(3.2)
Net liability for future policy benefits, after reinsurance recoverable	93.8	100.6	100.1
Impact of flooring on net liability for future policy benefits	0.0	0.0	0.0
Net liability for future policy benefits at September 30, 2023	$ 93.8	$ 100.6	$ 100.1