Investments (Schedule of Pre-tax Net Realized and Unrealized Gains on Equity Securities) (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
|
| Net realized and unrealized gains on equity securities recognized in income: | ||||
| On securities still held | $ 10.0 | $ 3.9 | $ 13.7 | $ 4.9 |
| On securities sold during the period | 0.8 | 0.2 | 2.3 | 0.6 |
| Total net realized and unrealized gains on equity securities recognized in income | $ 10.8 | $ 4.1 | $ 16.0 | $ 5.5 |