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Available-for-Sale and Held-to-Maturity 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 ($)	Dec. 21, 2024 USD ($)
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Allowance for credit losses	$ 0		$ 0
Accrued interest receivable	90,800,000		90,800,000			$ 92,600,000
Proceeds from sale of available-for-sale securities	0	$ 0	0	$ 0
Financial instruments pledged as collateral	$ 1,000,000,000		$ 1,000,000,000		$ 842,300,000
Number of available for sale securities whose amortized costs exceeded their fair values | Security	221		221
Available-for-sale Securities, Continuous	$ 117,189,000		$ 117,189,000
Available-for-sale Securities, Continuous Unrealized	116,086,000		116,086,000
Available-for-sale Securities, Continuous	$ 1,339,898,000		$ 1,339,898,000
Percentage of available-for-sale portfolio	79.30%		79.30%
Percentage available for sale securities	85.00%		85.00%
Pledged [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Trading securities pledged	$ 3,000,000,000		$ 3,000,000,000		2,200,000,000
Other Assets [Member]
Other Than Temporary Impairment Credit Losses Recognized In Earnings [Line Items]
Accrued interest receivable	$ 86,100,000		$ 86,100,000		$ 106,800,000

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