Securities (Investment Security Gains and 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] | ||||
| Gross Realized Debt Securities Gains | $ 0.0 | $ 0.1 | $ 0.0 | $ 185.2 |
| Gross Realized Debt Securities Losses | 0.0 | 0.0 | 0.0 | (374.5) |
| Investment Security Gains (Losses), net | $ 0.0 | $ 0.1 | $ 0.0 | $ (189.3) |