Investment Securities - Allowance for Credit Losses, Held-to-Maturity (Details) - USD ($) $ in Millions |
3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
Jun. 30, 2026 |
Jun. 30, 2025 |
Jun. 30, 2026 |
Jun. 30, 2025 |
|
| Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Roll Forward] | ||||
| Beginning balance | $ 12.9 | |||
| Ending balance | $ 13.8 | 13.8 | ||
| Tax-exempt | ||||
| Debt Securities, Held-to-Maturity, Allowance for Credit Loss [Roll Forward] | ||||
| Beginning balance | 13.4 | $ 11.6 | 12.9 | $ 16.4 |
| Provision for (recovery of) credit losses | 0.4 | 0.0 | 0.9 | (4.8) |
| Charge-offs | 0.0 | 0.0 | 0.0 | 0.0 |
| Recoveries | 0.0 | 0.0 | 0.0 | 0.0 |
| Ending balance | $ 13.8 | $ 11.6 | $ 13.8 | $ 11.6 |