Investments - Equity Securities Gains (Losses) (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2025 |
Jun. 30, 2024 |
Jun. 30, 2025 |
Jun. 30, 2024 |
|
| Investments, Debt and Equity Securities [Abstract] | ||||
| Net (losses) gains recognized during the period on equity securities | $ (7.9) | $ (10.0) | $ (18.2) | $ 5.5 |
| Less: net (losses) gains recognized during the period on equity securities sold, transferred or disposed during the period | 0.0 | (2.2) | 0.0 | 4.1 |
| Unrealized (losses) gains recognized during the reporting period on equity securities held at the reporting date | $ (7.9) | $ (7.8) | $ (18.2) | $ 1.4 |