Investments - Fair Value Changes to Equity Securities (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
|
| Investments, Debt and Equity Securities [Abstract] | ||||
| Net gains (losses) recognized on equity securities | $ (6.8) | $ 4.9 | $ (6.8) | $ 6.6 |
| Less: Net realized gains (losses) related to sales of equity securities | 0.0 | 0.1 | 0.0 | (13.9) |
| Total fair value changes to equity securities held | $ (6.8) | $ 4.8 | $ (6.8) | $ 20.5 |