Investment Securities - Allowance for Credit Losses, Held-to-Maturity (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2025 |
Jun. 30, 2024 |
Jun. 30, 2025 |
Jun. 30, 2024 |
|
| Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Roll Forward] | ||||
| Beginning balance | $ 16.4 | |||
| Ending balance | $ 11.6 | 11.6 | ||
| Tax-exempt | ||||
| Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Roll Forward] | ||||
| Beginning balance | 11.6 | $ 8.2 | 16.4 | $ 7.8 |
| Provision for (recovery of) credit losses | 0.0 | 0.5 | (4.8) | 0.9 |
| Charge-offs | 0.0 | 0.0 | 0.0 | 0.0 |
| Recoveries | 0.0 | 0.0 | 0.0 | 0.0 |
| Ending balance | $ 11.6 | $ 8.7 | $ 11.6 | $ 8.7 |