Summary of Accounting Policies and Accounting Changes (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reinsurance recoverables	$ 78.7	$ 86.5
Accrued investment income	81.9	88.4
Receivables from limited liability investments or partnership investments	0.3	0.0
Finite-lived intangible assets, net	266.1	268.9
Value of Business Acquired
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Finite-lived intangible assets, net	12.1	13.8
Customer Relationships
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Finite-lived intangible assets, net	1.5	1.7
Agent Relationships
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Finite-lived intangible assets, net	37.7	43.4
Other Receivables
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reinsurance recoverables	$ 24.3	$ 27.8