Long-Duration Insurance Contracts - Amounts Recognized in the Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	$ 57.7	$ 59.1	$ 116.9	$ 118.2
Interest expense	18.8	18.9	37.7	37.9
Whole Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	6.9	6.7	13.8	13.3
Interest expense	3.0	2.9	6.0	5.8
Term Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	11.0	11.4	22.2	22.2
Interest expense	1.3	1.2	2.6	2.4
Experience Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	7.7	7.9	15.4	16.1
Interest expense	10.8	10.9	21.6	21.9
Limited Pay Whole Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	1.6	1.7	3.4	3.3
Interest expense	0.7	0.7	1.4	1.3
Supplemental health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	30.0	30.0	60.4	59.7
Interest expense	1.9	2.1	3.9	4.3
Life Contingent SPIA Retirement Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	0.5	1.4	1.7	3.6
Interest expense	$ 1.1	$ 1.1	$ 2.2	$ 2.2