| **DEPOSITS AND OTHER CUSTOMER ACCOUNTS (Summary of Deposits and Other Customer Accounts) (Details) - USD ($) $ in Thousands** | Sep. 30, 2019 | Dec. 31, 2018 |
|-------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Balance**                                                                                                                   |          |          |
| Interest-bearing demand deposits                                                                                              | $ 10,376,161  | $ 8,827,704   |
| Non-interest-bearing demand deposits                                                                                          | 14,550,514    | 14,420,450    |
| Savings                                                                                                                       | 5,684,208     | 5,875,787     |
| Customer repurchase accounts                                                                                                  | 581,491       | 654,843       |
| Money market                                                                                                                  | 25,867,102    | 24,263,929    |
| Certificates of deposit (CDs)                                                                                                 | 9,180,492     | 7,468,667     |
| Total Deposits                                                                                                                | $ 66,239,968  | $ 61,511,380  |
| **Percent of total deposits**                                                                                                 |          |          |
| Interest-bearing demand deposits (as a percent)                                                                               | 15.70%        | 14.40%        |
| Non-interest-bearing demand deposits (as a percent)                                                                           | 22.00%        | 23.40%        |
| Savings (as a percent)                                                                                                        | 8.60%         | 9.60%         |
| Customer repurchase accounts (as a percent)                                                                                   | 0.90%         | 1.10%         |
| Money market (as a percent)                                                                                                   | 38.90%        | 39.40%        |
| CDs (as a percent)                                                                                                            | 13.90%        | 12.10%        |
| Total Deposits (as a percent)                                                                                                 | 100.00%       | 100.00%       |
| Foreign deposits                                                                                                              | $ 9,600,000   | $ 8,400,000   |

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| - Definition
The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.
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| - Definition
The aggregate of all foreign interest-bearing and noninterest-bearing deposit liabilities.
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| - Definition
Amount of deposits in accounts that offer many of the same services as checking accounts although transactions may be somewhat more limited, share some of the characteristics of a money market fund and are insured by the Federal government, also known as money market accounts.
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| - Definition
Amount of interest bearing deposits with no stated maturity, which may include passbook and statement savings accounts and money-market deposit accounts (MMDAs).
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| - Definition
The aggregate of all domestic and foreign interest-bearing deposit liabilities.
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| - Definition
The aggregate amount of all domestic and foreign noninterest-bearing deposits liabilities held by the entity.
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| - Definition
Amount of time deposit liabilities, including certificates of deposit.
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