Fair Value Disclosures - Carrying Value and Fair Value of the Financial Instruments that are Not Recognized or are Not Carried at Fair Value (Details) - Recurring - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Financial Assets
Other assets	$ 5.0	$ 6.4
Total financial assets	10,490.3	10,549.0
Level 1
Financial Assets
Other assets	0.0	0.0
Total financial assets	1,499.7	1,754.8
Level 2
Financial Assets
Other assets	0.0	0.0
Total financial assets	8,740.7	8,563.0
Level 3
Financial Assets
Other assets	5.0	6.4
Total financial assets	249.9	231.2
Carrying Value
Financial Assets
Commercial mortgage loans on real estate	309.5	324.7
Other investments	12.3	12.4
Other assets	27.1	31.3
Total financial assets	348.9	368.4
Financial Liabilities
Policy reserves under investment products (Individual and group annuities, subject to discretionary withdrawal)	1.8	1.8
Funds withheld under reinsurance	287.1	266.4
Debt	2,207.5	2,206.9
Total financial liabilities	2,496.4	2,475.1
Fair Value
Financial Assets
Commercial mortgage loans on real estate	306.0	323.1
Other investments	12.3	12.4
Other assets	27.1	31.3
Total financial assets	345.4	366.8
Financial Liabilities
Policy reserves under investment products (Individual and group annuities, subject to discretionary withdrawal)	1.7	1.8
Funds withheld under reinsurance	287.1	266.4
Debt	2,143.0	2,164.5
Total financial liabilities	2,431.8	2,432.7
Fair Value \| Level 1
Financial Assets
Commercial mortgage loans on real estate	0.0	0.0
Other investments	1.1	1.1
Other assets	0.0	0.0
Total financial assets	1.1	1.1
Financial Liabilities
Policy reserves under investment products (Individual and group annuities, subject to discretionary withdrawal)	0.0	0.0
Funds withheld under reinsurance	287.1	266.4
Debt	0.0	0.0
Total financial liabilities	287.1	266.4
Fair Value \| Level 2
Financial Assets
Commercial mortgage loans on real estate	0.0	0.0
Other investments	0.0	0.0
Other assets	0.0	0.0
Total financial assets	0.0	0.0
Financial Liabilities
Policy reserves under investment products (Individual and group annuities, subject to discretionary withdrawal)	0.0	0.0
Funds withheld under reinsurance	0.0	0.0
Debt	2,143.0	2,164.5
Total financial liabilities	2,143.0	2,164.5
Fair Value \| Level 3
Financial Assets
Commercial mortgage loans on real estate	306.0	323.1
Other investments	11.2	11.3
Other assets	27.1	31.3
Total financial assets	344.3	365.7
Financial Liabilities
Policy reserves under investment products (Individual and group annuities, subject to discretionary withdrawal)	1.7	1.8
Funds withheld under reinsurance	0.0	0.0
Debt	0.0	0.0
Total financial liabilities	$ 1.7	$ 1.8

Funds Held under Reinsurance Agreements, Liability, Fair Value Disclosure

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Fair value portion of asset recognized for present right to economic benefit.

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Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

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Fair value of financial and nonfinancial obligations.

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Fair value portion of other assets.

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