Long-Duration Insurance Contracts - Balances of and Changes in the LFPB (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2024	Sep. 30, 2023	Jun. 30, 2024	Dec. 31, 2023	Dec. 31, 2022
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Liability for Future Policy Benefit, before Reinsurance	$ 1,745.5	$ 1,745.5			$ 1,761.8
Whole Life Insurance
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	215.0	223.2
Beginning period (including reserves)						$ 215.1
Beginning balance at original discount rate	247.5	247.1
Beginning balance at original discount rate (including reserves)			$ 245.9
Change in cash flow assumptions				$ 0.0	0.0	0.0
Actual variances from expected experience				0.8	2.0	3.8
Adjusted balance				248.3	249.1	249.7
Issuances	3.3	8.8	10.8
Interest accruals	1.9	5.6	7.2
Net premiums collected	(5.8)	(15.8)	(20.6)
Ending balance at original discount rate	247.7	247.7
Effect of changes in discount rate assumptions	(20.9)	(20.9)			(23.9)
Ending balance	226.8	226.8
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	494.9	522.0
Beginning balance (including reserves)			493.6
Beginning balance at original discount rate	599.9	599.9		598.2	592.1
Beginning balance at original discount rate (including reserves)			581.9
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change				0.0	0.0	(0.6)
Actual variances from expected experience				0.7	2.1	4.0
Adjusted balance				598.9	594.2	585.3
Issuances	3.2	8.7	10.7
Interest accruals	5.0	14.7	19.0
Benefit payments	(7.2)	(17.7)	(22.9)
Ending balance at original discount rate	599.9	599.9
Effect of changes in discount rate assumptions	(68.9)	(68.9)			(70.1)
Ending balance	531.0	531.0
Liability for Future Policy Benefit, before Reinsurance	304.2	304.2			298.8
Less: Reinsurance recoverable	(63.8)	(63.8)			(64.3)
Net liability for future policy benefits, after reinsurance recoverable	240.4	240.4			234.5
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, 2024	240.4	240.4			234.5
Term Life Insurance
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	236.5	240.0
Beginning period (including reserves)						234.7
Beginning balance at original discount rate	261.8	256.6
Beginning balance at original discount rate (including reserves)			265.4
Change in cash flow assumptions				0.0	0.0	(16.8)
Actual variances from expected experience				0.2	0.3	(2.7)
Adjusted balance				262.0	256.9	245.9
Issuances	6.1	18.4	25.2
Interest accruals	2.7	8.0	10.3
Net premiums collected	(6.5)	(19.0)	(24.8)
Ending balance at original discount rate	264.3	264.3
Effect of changes in discount rate assumptions	(13.1)	(13.1)			(16.6)
Ending balance	251.2	251.2
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	364.4	370.1
Beginning balance (including reserves)			347.0
Beginning balance at original discount rate	422.2	422.2		417.4	405.4
Beginning balance at original discount rate (including reserves)			401.0
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change				0.0	0.0	(16.7)
Actual variances from expected experience				0.2	0.7	1.3
Adjusted balance				417.6	406.1	385.6
Issuances	6.0	18.6	25.8
Interest accruals	4.0	11.9	15.2
Benefit payments	(5.4)	(14.4)	(21.2)
Ending balance at original discount rate	422.2	422.2
Effect of changes in discount rate assumptions	(30.6)	(30.6)			(35.3)
Ending balance	391.6	391.6
Liability for Future Policy Benefit, before Reinsurance	140.3	140.3			130.2
Less: Reinsurance recoverable	(20.2)	(20.2)			(19.1)
Net liability for future policy benefits, after reinsurance recoverable	120.1	120.1			111.1
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, 2024	120.1	120.1			111.1
Experience Life Insurance
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	68.0	71.7
Beginning period (including reserves)						68.3
Beginning balance at original discount rate	66.4	67.0
Beginning balance at original discount rate (including reserves)			65.5
Change in cash flow assumptions				0.0	0.0	3.7
Actual variances from expected experience				(1.6)	(0.6)	0.7
Adjusted balance				64.8	66.4	69.9
Issuances	0.0	0.0	0.0
Interest accruals	0.9	2.8	3.7
Net premiums collected	(1.5)	(5.0)	(6.6)
Ending balance at original discount rate	64.2	64.2
Effect of changes in discount rate assumptions	4.8	4.8			4.7
Ending balance	69.0	69.0
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	825.3	883.0
Beginning balance (including reserves)			867.5
Beginning balance at original discount rate	785.0	785.0		788.4	797.5
Beginning balance at original discount rate (including reserves)			805.2
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change				0.0	0.0	5.0
Actual variances from expected experience				(2.2)	(0.6)	1.1
Adjusted balance				786.2	796.9	811.3
Issuances	0.0	0.0	0.0
Interest accruals	11.7	35.1	47.4
Benefit payments	(12.9)	(47.0)	(61.2)
Ending balance at original discount rate	785.0	785.0
Effect of changes in discount rate assumptions	84.6	84.6			85.5
Ending balance	869.6	869.6
Liability for Future Policy Benefit, before Reinsurance	800.6	800.6			811.3
Less: Reinsurance recoverable	(1.0)	(1.0)			(1.0)
Net liability for future policy benefits, after reinsurance recoverable	799.6	799.6			810.3
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, 2024	799.6	799.6			810.3
Limited Pay Whole Life Insurance
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	32.0	32.2
Beginning period (including reserves)						29.7
Beginning balance at original discount rate	34.5	33.9
Beginning balance at original discount rate (including reserves)			32.4
Change in cash flow assumptions				0.0	0.0	(0.2)
Actual variances from expected experience				(0.2)	(0.1)	1.0
Adjusted balance				34.3	33.8	33.2
Issuances	1.1	3.1	4.3
Interest accruals	0.3	1.0	1.2
Net premiums collected	(1.2)	(3.4)	(4.8)
Ending balance at original discount rate	34.5	34.5
Effect of changes in discount rate assumptions	(1.2)	(1.2)			(1.7)
Ending balance	33.3	33.3
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	85.6	89.6
Beginning balance (including reserves)			79.4
Beginning balance at original discount rate	110.1	110.1		108.8	105.6
Beginning balance at original discount rate (including reserves)			98.6
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change				0.0	0.0	(0.2)
Actual variances from expected experience				(0.1)	(0.1)	1.0
Adjusted balance				108.7	105.5	99.4
Issuances	0.9	3.0	4.3
Interest accruals	1.0	3.1	3.9
Benefit payments	(0.5)	(1.5)	(2.0)
Ending balance at original discount rate	110.1	110.1
Effect of changes in discount rate assumptions	(16.4)	(16.4)			(16.0)
Ending balance	93.7	93.7
Liability for Future Policy Benefit, before Reinsurance	60.3	60.3			57.4
Less: Reinsurance recoverable	(1.3)	(1.3)			(1.2)
Net liability for future policy benefits, after reinsurance recoverable	59.0	59.0			56.2
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, 2024	59.0	59.0			56.2
Supplemental health
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	180.2	182.0
Beginning period (including reserves)						167.4
Beginning balance at original discount rate	217.8	213.4
Beginning balance at original discount rate (including reserves)			205.1
Change in cash flow assumptions				0.0	0.0	6.5
Actual variances from expected experience				0.0	3.1	(1.6)
Adjusted balance				217.8	216.5	210.0
Issuances	4.5	14.7	19.4
Interest accruals	1.8	5.1	6.0
Net premiums collected	(5.9)	(18.1)	(22.0)
Ending balance at original discount rate	218.2	218.2
Effect of changes in discount rate assumptions	(28.3)	(28.3)			(31.4)
Ending balance	189.9	189.9
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	400.7	427.6
Beginning balance (including reserves)			431.7
Beginning balance at original discount rate	497.4	497.4		505.7	517.9
Beginning balance at original discount rate (including reserves)			537.1
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change				0.0	0.0	8.9
Actual variances from expected experience				(0.3)	2.7	(2.4)
Adjusted balance				505.4	520.6	543.6
Issuances	4.6	14.8	19.4
Interest accruals	3.7	10.9	14.4
Benefit payments	(16.3)	(48.9)	(59.5)
Ending balance at original discount rate	497.4	497.4
Effect of changes in discount rate assumptions	(84.0)	(84.0)			(90.3)
Ending balance	413.4	413.4
Liability for Future Policy Benefit, before Reinsurance	223.4	223.4			245.6
Less: Reinsurance recoverable	(4.2)	(4.2)			(4.0)
Net liability for future policy benefits, after reinsurance recoverable	219.2	219.2			241.6
Impact of flooring on net liability for future policy benefits	0.1	0.1			0.0
Net liability for future policy benefits at September 30, 2024	219.3	219.3			241.6
Cancer
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at September 30, 2024	110.7	110.7			92.7
Accident
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at September 30, 2024	20.9	20.9			21.4
Disability
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at September 30, 2024	26.6	26.6			23.5
Other
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at September 30, 2024	120.4	120.4			104.0
Life Contingent SPIA Retirement Insurance
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	1.1	2.2	5.6
Interest accruals	0.0	0.0	0.0
Net premiums collected	(1.1)	(2.2)	(5.6)
Ending balance at original discount rate	0.0	0.0
Effect of changes in discount rate assumptions	0.0	0.0			0.0
Ending balance	0.0	0.0
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	98.5	104.2
Beginning balance (including reserves)			103.3
Beginning balance at original discount rate	108.4	108.4		108.8	111.4
Beginning balance at original discount rate (including reserves)			113.4
Liability for Future Policy Benefit, Expected Future Policy Benefit, Cumulative Increase (Decrease) from Cash Flow Change				0.0	0.0	0.0
Actual variances from expected experience				0.1	0.2	(0.8)
Adjusted balance				$ 108.9	111.6	$ 112.6
Issuances	1.1	2.2	6.3
Interest accruals	1.1	3.2	4.4
Benefit payments	(2.7)	(8.6)	$ (11.9)
Ending balance at original discount rate	108.4	108.4
Effect of changes in discount rate assumptions	(5.6)	(5.6)			(7.2)
Ending balance	102.8	102.8
Liability for Future Policy Benefit, before Reinsurance	102.8	102.8			104.2
Less: Reinsurance recoverable	(3.7)	(3.7)			(3.6)
Net liability for future policy benefits, after reinsurance recoverable	99.1	99.1			100.6
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, 2024	$ 99.1	$ 99.1			$ 100.6