Long-Duration Insurance Contracts - Balances of and Changes in the LFPB (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2024	Jun. 30, 2023	Mar. 31, 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	$ 1,655.0	$ 1,655.0			$ 1,761.8
Whole Life Insurance
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	215.5	223.2
Beginning period (including reserves)						$ 215.1
Beginning balance at original discount rate	244.0	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				0.9	1.2	3.8
Adjusted balance				244.9	248.3	249.7
Issuances	3.0	5.5	10.8
Interest accruals	1.8	3.7	7.2
Net premiums collected	(2.2)	(10.0)	(20.6)
Ending balance at original discount rate	247.5	247.5
Effect of changes in discount rate assumptions	(32.5)	(32.5)			(23.9)
Ending balance	215.0	215.0
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	503.8	522.0
Beginning balance (including reserves)			493.6
Beginning balance at original discount rate	598.2	598.2		592.0	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				0.9	1.4	4.0
Adjusted balance				592.9	593.5	585.3
Issuances	3.0	5.5	10.7
Interest accruals	4.9	9.7	19.0
Benefit payments	(2.6)	(10.5)	(22.9)
Ending balance at original discount rate	598.2	598.2
Effect of changes in discount rate assumptions	(103.3)	(103.3)			(70.1)
Ending balance	494.9	494.9
Liability for Future Policy Benefit, before Reinsurance	280.0	280.0			298.8
Less: Reinsurance recoverable	(60.9)	(60.9)			(64.3)
Net liability for future policy benefits, after reinsurance recoverable	219.1	219.1			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 June 30, 2024	219.1	219.1			234.5
Term Life Insurance
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	237.7	240.0
Beginning period (including reserves)						234.7
Beginning balance at original discount rate	259.4	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)	0.1	(2.7)
Adjusted balance				259.2	256.7	245.9
Issuances	6.2	12.3	25.2
Interest accruals	2.7	5.3	10.3
Net premiums collected	(6.3)	(12.5)	(24.8)
Ending balance at original discount rate	261.8	261.8
Effect of changes in discount rate assumptions	(25.3)	(25.3)			(16.6)
Ending balance	236.5	236.5
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	366.1	370.1
Beginning balance (including reserves)			347.0
Beginning balance at original discount rate	417.4	417.4		411.1	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				(0.5)	0.5	1.3
Adjusted balance				410.6	405.9	385.6
Issuances	6.4	12.6	25.8
Interest accruals	4.0	7.9	15.2
Benefit payments	(3.6)	(9.0)	(21.2)
Ending balance at original discount rate	417.4	417.4
Effect of changes in discount rate assumptions	(53.0)	(53.0)			(35.3)
Ending balance	364.4	364.4
Liability for Future Policy Benefit, before Reinsurance	127.8	127.8			130.2
Less: Reinsurance recoverable	(19.3)	(19.3)			(19.1)
Net liability for future policy benefits, after reinsurance recoverable	108.5	108.5			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 June 30, 2024	108.5	108.5			111.1
Experience Life Insurance
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	69.0	71.7
Beginning period (including reserves)						68.3
Beginning balance at original discount rate	66.1	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				1.1	1.0	0.7
Adjusted balance				67.2	68.0	69.9
Issuances	0.0	0.0	0.0
Interest accruals	1.0	1.9	3.7
Net premiums collected	(1.8)	(3.5)	(6.6)
Ending balance at original discount rate	66.4	66.4
Effect of changes in discount rate assumptions	1.6	1.6			4.7
Ending balance	68.0	68.0
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	849.6	883.0
Beginning balance (including reserves)			867.5
Beginning balance at original discount rate	788.4	788.4		791.7	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				1.6	1.6	1.1
Adjusted balance				793.3	799.1	811.3
Issuances	0.0	0.0	0.0
Interest accruals	11.6	23.4	47.4
Benefit payments	(16.5)	(34.1)	(61.2)
Ending balance at original discount rate	788.4	788.4
Effect of changes in discount rate assumptions	36.9	36.9			85.5
Ending balance	825.3	825.3
Liability for Future Policy Benefit, before Reinsurance	757.3	757.3			811.3
Less: Reinsurance recoverable	(1.0)	(1.0)			(1.0)
Net liability for future policy benefits, after reinsurance recoverable	756.3	756.3			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 June 30, 2024	756.3	756.3			810.3
Limited Pay Whole Life Insurance
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	31.9	32.2
Beginning period (including reserves)						29.7
Beginning balance at original discount rate	34.2	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				(0.1)	0.1	1.0
Adjusted balance				34.1	34.0	33.2
Issuances	1.0	2.0	4.3
Interest accruals	0.4	0.7	1.2
Net premiums collected	(1.0)	(2.2)	(4.8)
Ending balance at original discount rate	34.5	34.5
Effect of changes in discount rate assumptions	(2.5)	(2.5)			(1.7)
Ending balance	32.0	32.0
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	87.2	89.6
Beginning balance (including reserves)			79.4
Beginning balance at original discount rate	108.8	108.8		107.3	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)	0.0	1.0
Adjusted balance				107.2	105.6	99.4
Issuances	1.1	2.1	4.3
Interest accruals	1.1	2.1	3.9
Benefit payments	(0.6)	(1.0)	(2.0)
Ending balance at original discount rate	108.8	108.8
Effect of changes in discount rate assumptions	(23.2)	(23.2)			(16.0)
Ending balance	85.6	85.6
Liability for Future Policy Benefit, before Reinsurance	53.6	53.6			57.4
Less: Reinsurance recoverable	(1.2)	(1.2)			(1.2)
Net liability for future policy benefits, after reinsurance recoverable	52.4	52.4			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 June 30, 2024	52.4	52.4			56.2
Supplemental health
Liability for Future Policy Benefit, Expected Net Premium [Roll Forward]
Beginning balance	179.5	182.0
Beginning period (including reserves)						167.4
Beginning balance at original discount rate	214.6	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				2.9	3.1	(1.6)
Adjusted balance				217.5	216.5	210.0
Issuances	4.6	10.2	19.4
Interest accruals	1.7	3.3	6.0
Net premiums collected	(6.0)	(12.2)	(22.0)
Ending balance at original discount rate	217.8	217.8
Effect of changes in discount rate assumptions	(37.6)	(37.6)			(31.4)
Ending balance	180.2	180.2
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Beginning balance	411.6	427.6
Beginning balance (including reserves)			431.7
Beginning balance at original discount rate	505.7	505.7		510.5	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				2.9	3.0	(2.4)
Adjusted balance				513.4	520.9	543.6
Issuances	4.6	10.2	19.4
Interest accruals	3.6	7.2	14.4
Benefit payments	(15.9)	(32.6)	(59.5)
Ending balance at original discount rate	505.7	505.7
Effect of changes in discount rate assumptions	(105.0)	(105.0)			(90.3)
Ending balance	400.7	400.7
Liability for Future Policy Benefit, before Reinsurance	220.4	220.4			245.6
Less: Reinsurance recoverable	(3.8)	(3.8)			(4.0)
Net liability for future policy benefits, after reinsurance recoverable	216.6	216.6			241.6
Impact of flooring on net liability for future policy benefits	0.0	0.0			0.0
Net liability for future policy benefits at June 30, 2024	216.6	216.6			241.6
Cancer
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at June 30, 2024	108.9	108.9			92.7
Accident
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at June 30, 2024	20.2	20.2			21.4
Disability
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at June 30, 2024	25.7	25.7			23.5
Other
Liability for Future Policy Benefit, Expected Future Policy Benefit [Roll Forward]
Net liability for future policy benefits at June 30, 2024	118.5	118.5			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	0.5	1.1	5.6
Interest accruals	0.0	0.0	0.0
Net premiums collected	(0.5)	(1.1)	(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	101.3	104.2
Beginning balance (including reserves)			103.3
Beginning balance at original discount rate	108.8	108.8		110.3	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				(0.2)	0.1	(0.8)
Adjusted balance				$ 110.1	111.5	$ 112.6
Issuances	0.5	1.1	6.3
Interest accruals	1.0	2.1	4.4
Benefit payments	(2.8)	(5.9)	$ (11.9)
Ending balance at original discount rate	108.8	108.8
Effect of changes in discount rate assumptions	(10.3)	(10.3)			(7.2)
Ending balance	98.5	98.5
Liability for Future Policy Benefit, before Reinsurance	98.5	98.5			104.2
Less: Reinsurance recoverable	(3.5)	(3.5)			(3.6)
Net liability for future policy benefits, after reinsurance recoverable	95.0	95.0			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 June 30, 2024	$ 95.0	$ 95.0			$ 100.6