Investments - Components of Equity Realized Gains (Losses) (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2025 |
Jun. 30, 2024 |
Jun. 30, 2025 |
Jun. 30, 2024 |
|
| Investments, Debt and Equity Securities [Abstract] | ||||
| Total net gains (losses) recognized during the period on equity securities | $ 358.0 | $ 92.0 | $ 173.0 | $ 392.0 |
| Less: Net gains (losses) recognized on equity securities sold during the period | 1.0 | (5.0) | 32.0 | 1.0 |
| Net holding period gains (losses) recognized during the period on equity securities held at period end | $ 357.0 | $ 97.0 | $ 141.0 | $ 391.0 |