Long-Duration Insurance Contracts - Undiscounted and Discounted Expected Gross Premiums and Expected Future Benefits and Expenses (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Whole life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	$ 524.0	$ 478.8
Expected future benefits and expenses, undiscounted	1,272.9	1,152.8
Expected future gross premiums, discounted	350.5	325.0
Expected future benefits and expenses, discounted	617.4	592.1
Term life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	712.1	689.0
Expected future benefits and expenses, undiscounted	736.2	682.7
Expected future gross premiums, discounted	464.2	449.4
Expected future benefits and expenses, discounted	433.2	405.4
Experience life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	497.8	530.0
Expected future benefits and expenses, undiscounted	1,639.0	1,703.1
Expected future gross premiums, discounted	279.3	296.1
Expected future benefits and expenses, discounted	782.8	797.5
Limited-Pay Whole Life
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	73.6	64.7
Expected future benefits and expenses, undiscounted	307.2	244.9
Expected future gross premiums, discounted	54.7	49.1
Expected future benefits and expenses, discounted	114.3	105.6
Supplemental health
Liability for Future Policy Benefit, by Product Segment [Line Items]
Expected future gross premiums, undiscounted	1,595.3	1,624.1
Expected future benefits and expenses, undiscounted	684.6	719.4
Expected future gross premiums, discounted	1,165.4	1,192.5
Expected future benefits and expenses, discounted	482.8	517.9
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	150.7	156.1
Expected future gross premiums, discounted	0.0	0.0
Expected future benefits and expenses, discounted	$ 107.3	$ 111.4