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Investment Securities - Investment Securities, Narrative (Details) |  | 3 Months Ended | 12 Months Ended
--- | --- | --- | ---
Mar. 12, 2023 USD ($) | Dec. 31, 2023 USD ($) loan | Dec. 31, 2022 USD ($) security loan | Dec. 31, 2021 USD ($)
Schedule of Investments [Line Items] |  |  |  |
Federal home loan bank stock | $ |  | $ 1,392,000,000 | $ 1,267,000,000 |
Federal reserve bank stock | $ |  | 203,000,000 | 176,000,000 |
Gross unrealized loss | $ |  | 0 | 2,000,000 | $ 0
Fair Value | $ |  | 9,145,000,000 | 9,060,000,000 |
Corporate bonds |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Fair Value | $ |  | $ 343,000,000 | $ 885,000,000 |
Signature Bank | Corporate bonds |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Fair Value | $ | $ 20,000,000 |  |  |
Collateralized Debt Obligations |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of securities continuous unrealized loss position more than twelve months | loan |  | 84 | 23 |
Capital trust notes |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of securities continuous unrealized loss position more than twelve months | security |  |  | 5 |
Number of securities continuous unrealized loss position more than twelve months | loan |  | 6 |  |
Asset-backed securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of securities continuous unrealized loss position more than twelve months | security |  |  | 7 |
Number of securities continuous unrealized loss position more than twelve months | loan |  | 8 |  |
Corporate bonds |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of securities continuous unrealized loss position more than twelve months | security |  |  | 2 |
Number of securities continuous unrealized loss position more than twelve months | loan |  | 12 |  |
Corporate bonds | Signature Bank |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Provision for credit loss | $ | $ 20,000,000 |  |  |
US Government Agencies Debt Securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of securities continuous unrealized loss position more than twelve months | loan |  | 37 | 33 |
Mortgage- Related Securities |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of securities continuous unrealized loss position more than twelve months | loan |  | 302 | 133 |
Mutual funds |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of securities continuous unrealized loss position more than twelve months | security |  |  | 1 |
Number of securities continuous unrealized loss position more than twelve months | loan |  | 1 |  |
Municipal bonds |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of securities continuous unrealized loss position more than twelve months | security |  |  | 1 |
Number of securities continuous unrealized loss position more than twelve months | loan |  | 1 |  |
Foreign notes |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Number of securities continuous unrealized loss position more than twelve months | loan |  | 1 |  |
Federal Home Loan Bank of New York |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Federal home loan bank stock | $ |  | $ 861,000,000 | $ 762,000,000 |
Federal Home Loan Bank of Indianapolis |  |  |  |
Schedule of Investments [Line Items] |  |  |  |
Federal home loan bank stock | $ |  | $ 329,000,000 | $ 329,000,000 |

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