Securities (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2025 USD ($) security	Sep. 30, 2024 USD ($)	Sep. 30, 2025 USD ($) security	Sep. 30, 2024 USD ($)	Dec. 31, 2024 USD ($) security
Debt and Equity Securities, FV-NI [Line Items]
Negative provision of credit losses	$ (900,000)	$ (400,000)	$ (200,000)	$ (1,000,000.0)
Number of securities in an unrealized loss position | security	729		729		767
Total fair value	$ 14,170,300,000		$ 14,170,300,000		$ 17,832,200,000
Debt securities, unrealized losses	$ 168,800,000		$ 168,800,000		$ 255,100,000
Percentage of debt securities, held-to-maturity, portfolio	1		1		1
Proceeds from sale of investment securities	$ 0	0	$ 0	2,000,000,000.0
Investment security gain (loss), net	$ 0	0	$ 0	(189,300,000)
Rating of A or higher
Debt and Equity Securities, FV-NI [Line Items]
Percentage of debt securities, held-to-maturity, portfolio	0.95		0.95		0.96
Sub-Sovereign, Supranational, Non US Agency Bonds and Corporate Debt Securities
Debt and Equity Securities, FV-NI [Line Items]
Allowance for credit losses for AFS securities	$ 0		$ 0
Corporate Debt
Debt and Equity Securities, FV-NI [Line Items]
Allowance for credit losses for AFS securities					$ 200,000
Total fair value	106,900,000		106,900,000		76,900,000
Debt securities, unrealized losses	800,000		800,000		$ 1,600,000
Investment security gain (loss), net	$ 0	$ 0	$ 0	$ 0