Securities (Investment Security Gains and Losses by Security Type) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Schedule of Held-to-maturity Securities [Line Items]
Investment Security Gains (Losses), net	$ (189.3)	$ (169.5)	$ (214.0)
U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Investment Security Gains (Losses), net	(34.8)	(29.9)	0.0
Obligations of States and Political Subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Investment Security Gains (Losses), net	0.0	9.8	(95.8)
Government Sponsored Agency
Schedule of Held-to-maturity Securities [Line Items]
Investment Security Gains (Losses), net	(23.0)	(73.2)	0.0
Corporate Debt
Schedule of Held-to-maturity Securities [Line Items]
Investment Security Gains (Losses), net	0.0	(7.6)	(67.3)
Covered Bonds
Schedule of Held-to-maturity Securities [Line Items]
Investment Security Gains (Losses), net	(4.2)	0.0	0.0
Other Asset-Backed
Schedule of Held-to-maturity Securities [Line Items]
Investment Security Gains (Losses), net	(56.5)	(58.6)	(17.1)
Commercial Mortgage-Backed
Schedule of Held-to-maturity Securities [Line Items]
Investment Security Gains (Losses), net	(22.6)	(0.9)	(33.8)
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Schedule of Held-to-maturity Securities [Line Items]
Investment Security Gains (Losses), net	$ (48.2)	$ (9.1)	0.0
AFS debt securities for sale
Schedule of Held-to-maturity Securities [Line Items]
Investment Security Gains (Losses), net			$ (213.0)