Long-Duration Insurance Contracts - Amounts Recognized in the Statement of Operations (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	$ 60.1	$ 60.0	$ 178.3	$ 178.3
Interest expense	18.9	18.8	56.8	56.8
Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	7.2	7.0	20.5	19.3
Interest expense	3.0	2.8	8.8	8.4
Term Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	11.7	11.3	33.9	31.6
Interest expense	1.2	1.0	3.6	3.2
Experience Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	8.1	8.4	24.2	25.2
Interest expense	10.9	11.1	32.8	33.2
Limited Pay Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	2.2	2.0	5.5	6.3
Interest expense	0.6	0.6	1.9	1.8
Supplemental health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	30.0	30.4	89.7	91.7
Interest expense	2.1	2.2	6.4	6.9
SPIA (life contingent)
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	0.9	0.9	4.5	4.2
Interest expense	$ 1.1	$ 1.1	$ 3.3	$ 3.3