| **DEPOSITS AND OTHER CUSTOMER ACCOUNTS (Tables)** | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
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| **Deposits [Abstract]**                           |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
| Summary of Deposits and Other Customer Accounts   | Deposits and other customer accounts are summarized as follows: June 30, 2016 December 31, 2015 Balance Percent of total deposits Balance Percent of total deposits (in thousands)Interest-bearing demand deposits$8,877,518 15.7% $10,253,948 18.3%Non-interest-bearing demand deposits9,919,471 17.5% 8,240,023 14.7%Savings4,102,768 7.3% 3,956,165 7.0%Customer repurchase accounts833,882 1.5% 896,736 1.6%Money market24,468,371 43.3% 24,254,357 43.2%Certificates of deposit8,295,689 14.7% 8,513,003 15.2%Total Deposits (1)$56,497,699 100% $56,114,232 100%(1)  Includes foreign deposits of $558.0 million and $495.9 million at June 30, 2016 and December 31, 2015, respectively. |

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