Long-Duration Insurance Contracts - Undiscounted and Discounted Expected Gross Premiums and Expected Future Benefits and Expenses (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	$ 525.6	$ 524.0
Expected future benefits and expenses, undiscounted	1,279.8	1,272.9
Expected future gross premiums, discounted	350.7	350.5
Expected future benefits and expenses, discounted	618.2	617.4
Term Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	715.4	712.1
Expected future benefits and expenses, undiscounted	745.1	736.2
Expected future gross premiums, discounted	464.8	464.2
Expected future benefits and expenses, discounted	437.3	433.2
Experience life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	487.5	497.8
Expected future benefits and expenses, undiscounted	1,619.8	1,639.0
Expected future gross premiums, discounted	273.8	279.3
Expected future benefits and expenses, discounted	776.3	782.8
Limited-Pay Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	72.6	73.6
Expected future benefits and expenses, undiscounted	309.0	307.2
Expected future gross premiums, discounted	53.9	54.7
Expected future benefits and expenses, discounted	115.1	114.3
Supplemental health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	1,589.6	1,595.3
Expected future benefits and expenses, undiscounted	683.7	684.6
Expected future gross premiums, discounted	1,158.6	1,165.4
Expected future benefits and expenses, discounted	480.1	482.8
SPIA (life contingent)
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	0.0	0.0
Expected future benefits and expenses, undiscounted	148.8	150.7
Expected future gross premiums, discounted	0.0	0.0
Expected future benefits and expenses, discounted	$ 106.0	$ 107.3