Available-for-Sale and Held-to-Maturity Securities (Narrative) (Details)	3 Months Ended
	Mar. 31, 2024 USD ($) Security	Mar. 31, 2023 USD ($)	Dec. 31, 2023 USD ($)	Dec. 21, 2023 USD ($)
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Accrued interest receivable	$ 96,800,000			$ 94,000,000
Debt Securities, Available-for-Sale, Allowance for Credit Loss	0
Proceeds from sale of available-for-sale securities	0	$ 2,400,000
Net realized gains (loss) resulting from sale of available-for-sale securities		$ 7,600,000
Financial instruments pledged as collateral	$ 713,700,000		$ 746,400,000
Number of available for sale securities whose amortized costs exceeded their fair values | Security	276
Available-for-sale Securities, Continuous	$ 187,232,000
Available-for-sale Securities, Continuous Unrealized	186,073,000
Available-for-sale Securities, Continuous	$ 1,471,597,000
Percentage of available-for-sale portfolio	98.10%
Pledged [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Trading securities pledged	$ 1,300,000,000		1,300,000,000
Other Assets [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Accrued interest receivable	$ 89,700,000		$ 95,700,000