Long-Duration Insurance Contracts - Amounts Recognized in the Statement of Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	$ 237.0	$ 239.0
Interest expense	75.2	75.7
Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	28.1	28.1
Interest expense	12.2	11.8
Term Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	45.9	45.2
Interest expense	5.3	4.8
Experience life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	30.6	32.1
Interest expense	43.0	43.7
Limited-Pay Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	7.2	7.2
Interest expense	2.8	2.6
Supplemental health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	121.6	120.3
Interest expense	7.6	8.4
SPIA (life contingent)
Liability for Future Policy Benefit, by Product Segment [Line Items]
Gross premiums or assessments	3.6	6.1
Interest expense	$ 4.3	$ 4.4