Investment Securities - Investment Gains (Losses) for Level 3 (Details) - Other long-term investments - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
|
| Gain (Loss) on Securities [Line Items] | ||||
| Total net unrealized investment gains (losses) recognized during the period on Level 3 investments held at the end of period | $ 77.6 | $ 40.8 | $ 133.7 | $ 87.0 |
| Level 3 | ||||
| Gain (Loss) on Securities [Line Items] | ||||
| Total net unrealized investment gains (losses) recognized during the period on Level 3 investments held at the end of period | $ 77.5 | $ 18.4 | $ 123.8 | $ 63.4 |