Investments - Offsetting of Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Asset derivatives
Net Amounts of Assets/ Liabilities Presented in the Consolidated Balance Sheets	$ 19.0	$ 6.8
Free-standing derivatives
Asset derivatives
Gross Amounts	19.0	6.8
Gross Amounts Offset in the Consolidated Balance Sheets	0.0	0.0
Net Amounts of Assets/ Liabilities Presented in the Consolidated Balance Sheets	19.0	6.8
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	18.5	5.9
Net Amount	$ 0.5
Net Amount		$ 0.9