Investments (Schedule of Pre-tax Net Realized and Unrealized Gains (losses)on Equity Securities) (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
|
| Net realized and unrealized gains (losses) on equity securities recognized in income: | ||||
| On securities sold during the period | $ 3.2 | $ 0.0 | $ 5.5 | $ 0.6 |
| On securities still held | (10.0) | 11.2 | 3.7 | 16.1 |
| Total net realized and unrealized gains (losses) on equity securities recognized in income | $ (6.8) | $ 11.2 | $ 9.2 | $ 16.7 |