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Investment Securities - Pledged Securities and Concentration Narrative (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2024 | Dec. 31, 2023
Concentration of risk |  |
Credit losses recognized on securities | $ 0 | $ 0
Asset Pledged as Collateral |  |
Financial Instruments Owned and Pledged as Collateral |  |
Investment securities pledged as collateral | 4,300,000,000 | 5,000,000,000.0
Asset Pledged as Collateral | Public deposits |  |
Financial Instruments Owned and Pledged as Collateral |  |
Investment securities pledged as collateral | 1,900,000,000 | 2,600,000,000
Asset Pledged as Collateral | Other financial transactions |  |
Financial Instruments Owned and Pledged as Collateral |  |
Investment securities pledged as collateral | 154,000,000.0 | 183,000,000.0
Borrowing Capacity |  |
Financial Instruments Owned and Pledged as Collateral |  |
Investment securities pledged as collateral | 2,200,000,000 | 2,300,000,000
Non-government issuer |  |
Concentration of risk |  |
Securities of issuers in excess of 10% of stockholders' equity | $ 0 | $ 0

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- Definition Amount, after allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity), and investment in debt security measured at fair value with change in fair value recognized in net income (trading). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 210 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03(a)(1)(a)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479440/944-210-S99-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481830/320-10-45-1 + Details
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- Definition Amount of increase (decrease) in allowance for credit loss of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 326 -SubTopic 30 -Name Accounting Standards Codification -Section 50 -Paragraph 9 -Publisher FASB -URI https://asc.fasb.org//1943274/2147479106/326-30-50-9 + Details
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- Definition This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 825 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 20 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482907/825-10-50-20 + Details
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