Investments - Offsetting of Assets and Liabilities (Details) - Free-standing derivatives - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Asset derivatives:
Gross Amounts	$ 19.4	$ 19.0
Gross Amounts Offset in the Consolidated Balance Sheets	0.0	0.0
Net Amounts of Assets/ Liabilities Presented in the Consolidated Balance Sheets	19.4	19.0
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	20.2	18.5
Net Amount	$ (0.8)
Net Amount		$ 0.5