|**DEPOSITS AND OTHER CUSTOMER ACCOUNTS (Tables)** | 3 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              
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|**Deposits [Abstract]**                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Summary of Deposits and Other Customer Accounts   | Deposits and other customer accounts are summarized as follows at the dates indicated:March 31, 2023December 31, 2022(dollars in thousands)BalancePercent of total depositsBalancePercent of total depositsInterest-bearing demand deposits$12,712,25616.0%$12,950,73716.4%Non-interest-bearing demand deposits17,855,52322.5%18,082,06122.9%Savings5,129,9216.5%5,282,2596.7%Customer repurchase accounts333,9550.4%338,4210.4%Money market27,513,37634.7%29,369,82737.0%CDs15,749,82819.9%13,105,23616.6%Total deposits(1)$79,294,859100.0%$79,128,541100.0%(1)  Includes foreign deposits, as defined by the FRB, of $6.5 billion and $5.9 billion at March 31, 2023 and December 31, 2022, respectively.
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|(dollars in thousands)                            |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Interest-bearing demand deposits                  |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Non-interest-bearing demand deposits              |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Savings                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Customer repurchase accounts                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Money market                                      |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|CDs                                               |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             
|Total deposits(1)                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             

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