Schedule 2 - Parent Company Financial Statements - Balance Sheets (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Amortized cost of fixed maturities	$ 7,475.7	$ 7,295.0
Cost of equity securities	287.9	197.1
Long-term Debt	$ 868.0	1,278.4
Senior Notes \| Senior Notes, 4.35 Percent Due February 15, 2025
Stated interest rate, percentage	4.35%
Parent Company
Amortized cost of fixed maturities	$ 0.5	0.5
Cost of equity securities	$ 13.8	12.8
Parent Company \| Senior Notes \| Senior Notes, 4.35 Percent Due February 15, 2025
Stated interest rate, percentage	4.35%
Long-term Debt	$ 0.0	448.1
Parent Company \| Senior Notes \| Senior Notes, 2.400 Percent Due September 30, 2030
Stated interest rate, percentage	2.40%
Long-term Debt	$ 358.1	338.9
Parent Company \| Senior Notes \| Senior Notes, 3.800 Percent Due February 23, 2032
Stated interest rate, percentage	3.80%
Long-term Debt	$ 369.4	352.2
Parent Company \| Junior Debt \| 5.875% Fixed-Rate Reset Junior Subordinated Debentures due 2062
Stated interest rate, percentage	5.875%
Long-term Debt	$ 140.4	$ 139.2

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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