Available-for-Sale and Held-to-Maturity Securities (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($) Security	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) Security	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Accrued interest receivable	$ 78,200,000		$ 78,200,000		$ 65,700,000
Proceeds from sale of available-for-sale securities	0	$ 80,000,000	10,000,000	$ 80,000,000
Net realized gains (loss) resulting from sale of available-for-sale securities		$ 100,000	(7,600,000)	$ 100,000
Financial instruments pledged as collateral	$ 721,000,000		$ 721,000,000		796,200,000
Number of available for sale securities whose amortized costs exceeded their fair values | Security	284		284
Available-for-sale Securities, Continuous	$ 250,511,000		$ 250,511,000
Available-for-sale Securities, Continuous Unrealized	247,335,000		247,335,000
Available-for-sale Securities, Continuous	$ 1,509,735,000		$ 1,509,735,000
Percentage of available-for-sale portfolio	99.80%		99.80%
Held-to-Maturity, allowance for credit Loss	$ 0		$ 0
Available-for-Sale, allowance for credit Loss	0		0
Pledged [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Trading securities pledged	1,300,000,000		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	$ 94,800,000		$ 94,800,000		$ 82,300,000