Long-Duration Insurance Contracts - Undiscounted and Discounted Expected Gross Premiums and Expected Future Benefits and Expenses (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	$ 552.0	$ 524.0
Expected future benefits and expenses, undiscounted	1,347.4	1,272.9
Expected future gross premiums, discounted	362.8	350.5
Expected future benefits and expenses, discounted	629.4	617.4
Term Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	689.2	712.1
Expected future benefits and expenses, undiscounted	728.1	736.2
Expected future gross premiums, discounted	455.5	464.2
Expected future benefits and expenses, discounted	425.8	433.2
Experience life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	461.9	497.8
Expected future benefits and expenses, undiscounted	1,549.5	1,639.0
Expected future gross premiums, discounted	261.1	279.3
Expected future benefits and expenses, discounted	768.9	782.8
Limited-Pay Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	75.6	73.6
Expected future benefits and expenses, undiscounted	335.2	307.2
Expected future gross premiums, discounted	55.9	54.7
Expected future benefits and expenses, discounted	117.5	114.3
Supplemental health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	1,607.5	1,595.3
Expected future benefits and expenses, undiscounted	675.5	684.6
Expected future gross premiums, discounted	1,162.1	1,165.4
Expected future benefits and expenses, discounted	466.2	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	146.4	150.7
Expected future gross premiums, discounted	0.0	0.0
Expected future benefits and expenses, discounted	$ 104.2	$ 107.3