Securities (Narrative) (Details)	Sep. 30, 2023 USD ($) Security	Dec. 31, 2022 USD ($) Security
Debt and Equity Securities, FV-NI [Line Items]
Securities with an aggregate fair value	$ 5,183,981,000	$ 5,483,762,000
Securities available for sale, amortized cost	6,085,309,000	6,310,214,000
Securities classified as trading	0	$ 0
Allowance for credit loss	$ 0
Securities that met the criteria of a credit loss event | Security	0
Number of securities with market values below their cost basis | Security	787	757
Asset Pledged as Collateral without Right [Member]
Debt and Equity Securities, FV-NI [Line Items]
Securities pledged as collateral	$ 4,300,000,000	$ 4,900,000,000
Available for Sale and Held to Maturity [Member]
Debt and Equity Securities, FV-NI [Line Items]
Amortized cost of securities excluding accrued interest	$ 28,200,000	$ 29,100,000