Investments - Equity Securities Gains (Losses) (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
|
| Investments, Debt and Equity Securities [Abstract] | ||||
| Net gains (losses) recognized during the period on equity securities | $ 86.8 | $ (7.9) | $ 86.4 | $ (18.2) |
| Less: net gains (losses) recognized during the period on equity securities sold, transferred or disposed during the period | 3.4 | 0.0 | 3.0 | 0.0 |
| Unrealized gains (losses) recognized during the reporting period on equity securities held at the reporting date | $ 83.4 | $ (7.9) | $ 83.4 | $ (18.2) |