Investments - Offsetting of Assets and Liabilities (Details) - Free-standing derivatives - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Asset derivatives:
Gross Amounts	$ 19.5	$ 18.5
Gross Amounts Offset in the Consolidated Balance Sheets	0.0	0.0
Net Amounts of Assets/ Liabilities Presented in the Consolidated Balance Sheets	19.5	18.5
Gross Amounts Not Offset in the Consolidated Balance Sheets, Financial Instruments	0.0	0.0
Gross Amounts Not Offset in the Consolidated Balance Sheets, Cash Collateral Received	18.2	20.4
Net Amount	$ 1.3	$ (1.9)