Investments - Schedule of Allowance for Expected Credit Losses (Details) - USD ($) $ in Millions |
3 Months Ended | 9 Months Ended | ||
|---|---|---|---|---|
Sep. 30, 2026 |
Sep. 30, 2025 |
Sep. 30, 2026 |
Sep. 30, 2025 |
|
| Debt Securities, Available-for-Sale, Allowance for Credit Loss [Roll Forward] | ||||
| Balance at beginning of period | $ 3.6 | $ 0.6 | $ 0.6 | $ 5.9 |
| Expected credit losses on securities where credit losses were not previously recognized | 10.6 | 0.4 | 14.5 | 1.1 |
| Additions/(reductions) for expected credit losses on securities where credit losses were previously recognized | 5.4 | (0.6) | 5.2 | (5.8) |
| Securities sold/redeemed/matured | (0.3) | (0.1) | (1.0) | (0.9) |
| Balance at end of period | $ 19.3 | $ 0.3 | $ 19.3 | $ 0.3 |