Long-Duration Insurance Contracts - Balances of and Changes in the LFPB (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2025	Dec. 31, 2024	Jun. 30, 2025	Dec. 31, 2023
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits	$ 1,636.8	$ 1,636.8	$ 1,622.8
Whole Life
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	234.4	229.1	223.2
Beginning balance at original discount rate	264.7	263.2	247.1
Change in cash flow assumptions			6.3	$ 6.3	$ 13.8
Actual variances from expected experience			1.3	0.0	3.2
Adjusted balance			270.8	271.0	264.1
Issuances	2.1	8.0	12.6
Interest accruals	2.2	6.3	7.6
Net premiums collected	(5.3)	(15.1)	(21.1)
Ending balance at original discount rate	270.0	270.0	263.2
Effect of changes in discount rate assumptions	(27.9)	(27.9)	(34.1)
Ending balance	242.1	242.1	229.1
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	514.0	504.3	522.0
Beginning balance at original discount rate	629.4	629.4	617.4	622.1	592.1
Changes in cash flow assumptions			5.9	5.9	13.7
Actual variances from expected experience			1.9	(0.1)	3.4
Adjusted balance			625.2	627.9	609.2
Issuances	2.1	8.0	12.6
Interest accruals	5.3	15.7	19.8
Benefit payments	(5.9)	(19.5)	(24.2)
Ending balance at original discount rate	629.4	629.4	617.4
Effect of changes in discount rate assumptions	(101.2)	(101.2)	(113.1)
Ending balance	528.2	528.2	504.3
Net liability for future policy benefits	286.0	286.0	275.2
Less: Reinsurance recoverable	(60.7)	(60.7)	(60.2)
Net liability for future policy benefits, after reinsurance recoverable	225.3	225.3	215.0
Impact of flooring on net liability for future policy benefits	0.0	0.0	0.0
Net liability for future policy benefits	225.3	225.3	215.0
Term Life
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	253.2	245.9	240.0
Beginning balance at original discount rate	273.3	271.2	256.6
Change in cash flow assumptions			(16.5)	(16.5)	4.6
Actual variances from expected experience			(1.7)	0.3	(0.5)
Adjusted balance			253.0	257.1	260.7
Issuances	5.8	17.5	25.2
Interest accruals	2.8	8.4	10.7
Net premiums collected	(6.3)	(19.5)	(25.4)
Ending balance at original discount rate	259.4	259.4	271.2
Effect of changes in discount rate assumptions	(13.8)	(13.8)	(25.3)
Ending balance	245.6	245.6	245.9
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	394.2	377.8	370.1
Beginning balance at original discount rate	425.8	425.8	433.2	442.4	405.4
Changes in cash flow assumptions			(20.7)	(20.7)	5.6
Actual variances from expected experience			(2.0)	0.6	(1.0)
Adjusted balance			410.5	422.3	410.0
Issuances	5.9	17.7	25.5
Interest accruals	4.2	12.8	16.1
Benefit payments	(6.6)	(15.2)	(18.4)
Ending balance at original discount rate	425.8	425.8	433.2
Effect of changes in discount rate assumptions	(38.1)	(38.1)	(55.4)
Ending balance	387.7	387.7	377.8
Net liability for future policy benefits	142.1	142.1	131.8
Less: Reinsurance recoverable	(20.2)	(20.2)	(19.3)
Net liability for future policy benefits, after reinsurance recoverable	121.9	121.9	112.5
Impact of flooring on net liability for future policy benefits	0.0	0.0	0.0
Net liability for future policy benefits	121.9	121.9	112.5
Experience life
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	67.6	66.6	71.7
Beginning balance at original discount rate	65.4	65.4	67.0
Change in cash flow assumptions			0.7	0.7	1.5
Actual variances from expected experience			1.9	0.3	0.0
Adjusted balance			68.0	66.4	68.5
Issuances	0.0	0.0	0.0
Interest accruals	1.0	2.8	3.7
Net premiums collected	(1.8)	(5.2)	(6.8)
Ending balance at original discount rate	65.6	65.6	65.4
Effect of changes in discount rate assumptions	3.1	3.1	1.2
Ending balance	68.7	68.7	66.6
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	810.7	813.2	883.0
Beginning balance at original discount rate	768.9	768.9	782.8	771.8	797.5
Changes in cash flow assumptions			1.7	1.7	2.2
Actual variances from expected experience			3.7	0.5	0.2
Adjusted balance			788.2	774.0	799.9
Issuances	0.0	0.0	0.0
Interest accruals	11.4	34.4	46.7
Benefit payments	(16.5)	(53.7)	(63.8)
Ending balance at original discount rate	768.9	768.9	782.8
Effect of changes in discount rate assumptions	52.1	52.1	30.4
Ending balance	821.0	821.0	813.2
Net liability for future policy benefits	752.3	752.3	746.6
Less: Reinsurance recoverable	(0.8)	(0.8)	(0.9)
Net liability for future policy benefits, after reinsurance recoverable	751.5	751.5	745.7
Impact of flooring on net liability for future policy benefits	0.0	0.0	0.0
Net liability for future policy benefits	751.5	751.5	745.7
Limited-Pay Whole Life
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	34.2	34.2	32.2
Beginning balance at original discount rate	36.1	36.8	33.9
Change in cash flow assumptions			0.4	0.4	2.2
Actual variances from expected experience			0.2	0.4	0.0
Adjusted balance			37.4	36.9	36.1
Issuances	0.9	1.9	4.0
Interest accruals	0.4	1.1	1.4
Net premiums collected	(1.2)	(3.4)	(4.7)
Ending balance at original discount rate	37.0	37.0	36.8
Effect of changes in discount rate assumptions	(1.6)	(1.6)	(2.6)
Ending balance	35.4	35.4	34.2
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	88.8	86.2	89.6
Beginning balance at original discount rate	117.5	117.5	114.3	116.4	105.6
Changes in cash flow assumptions			0.2	0.2	2.4
Actual variances from expected experience			0.4	0.5	0.0
Adjusted balance			114.9	117.1	108.0
Issuances	0.9	1.9	4.0
Interest accruals	1.2	3.4	4.2
Benefit payments	(1.7)	(2.7)	(1.9)
Ending balance at original discount rate	117.5	117.5	114.3
Effect of changes in discount rate assumptions	(26.4)	(26.4)	(28.1)
Ending balance	91.1	91.1	86.2
Net liability for future policy benefits	55.7	55.7	52.1
Less: Reinsurance recoverable	(1.3)	(1.3)	(1.4)
Net liability for future policy benefits, after reinsurance recoverable	54.4	54.4	50.7
Impact of flooring on net liability for future policy benefits	0.0	0.0	0.0
Net liability for future policy benefits	54.4	54.4	50.7
Supplemental health
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	186.2	179.9	182.0
Beginning balance at original discount rate	216.6	214.6	213.4
Change in cash flow assumptions			(2.8)	(2.8)	(5.2)
Actual variances from expected experience			(0.4)	1.1	2.9
Adjusted balance			211.4	214.9	211.1
Issuances	4.9	17.6	20.9
Interest accruals	1.7	5.2	6.8
Net premiums collected	(6.3)	(19.0)	(24.2)
Ending balance at original discount rate	215.2	215.2	214.6
Effect of changes in discount rate assumptions	(26.6)	(26.6)	(34.7)
Ending balance	188.6	188.6	179.9
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	384.7	383.4	427.6
Beginning balance at original discount rate	466.2	466.2	482.8	476.8	517.9
Changes in cash flow assumptions			(5.3)	(5.3)	(6.5)
Actual variances from expected experience			(1.7)	1.4	2.5
Adjusted balance			475.8	472.9	513.9
Issuances	4.9	17.6	20.9
Interest accruals	3.4	10.4	14.4
Benefit payments	(15.0)	(37.6)	(66.4)
Ending balance at original discount rate	466.2	466.2	482.8
Effect of changes in discount rate assumptions	(83.2)	(83.2)	(99.4)
Ending balance	383.0	383.0	383.4
Net liability for future policy benefits	194.5	194.5	203.5
Less: Reinsurance recoverable	(4.9)	(4.9)	(4.7)
Net liability for future policy benefits, after reinsurance recoverable	189.6	189.6	198.8
Impact of flooring on net liability for future policy benefits	0.0	0.0	0.0
Net liability for future policy benefits	189.6	189.6	198.8
Cancer
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits	67.3	67.3	72.2
Accident
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits	18.3	18.3	18.8
Disability
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits	21.3	21.3	21.4
Other
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits	82.7	82.7	86.4
SPIA (life contingent)
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
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	0.5	1.8	2.8
Interest accruals	0.0	0.0	0.0
Net premiums collected	(0.5)	(1.8)	(2.8)
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	97.1	97.3	104.2
Beginning balance at original discount rate	104.2	104.2	107.3	105.2	111.4
Changes in cash flow assumptions			0.0	0.0	0.0
Actual variances from expected experience			0.0	0.0	0.2
Adjusted balance			107.3	$ 105.2	$ 111.6
Issuances	0.5	1.8	2.8
Interest accruals	1.0	3.1	4.3
Benefit payments	(2.5)	(8.0)	(11.4)
Ending balance at original discount rate	104.2	104.2	107.3
Effect of changes in discount rate assumptions	(6.7)	(6.7)	(10.0)
Ending balance	97.5	97.5	97.3
Net liability for future policy benefits	97.5	97.5	97.3
Less: Reinsurance recoverable	(3.9)	(3.9)	(3.5)
Net liability for future policy benefits, after reinsurance recoverable	93.6	93.6	93.8
Impact of flooring on net liability for future policy benefits	0.0	0.0	0.0
Net liability for future policy benefits	$ 93.6	$ 93.6	$ 93.8