| **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: March 31, 2016 December 31, 2015 Balance Percent of total deposits Balance Percent of total deposits (in thousands)Interest-bearing demand deposits$9,804,755 17.1% $10,253,948 18.3%Non-interest-bearing demand deposits8,565,569 14.9% 8,240,023 14.7%Savings4,149,767 7.2% 3,956,165 7.0%Customer repurchase accounts879,411 1.5% 896,736 1.6%Money market24,589,904 42.8% 24,254,357 43.2%Certificates of deposit9,474,844 16.5% 8,513,003 15.2%Total Deposits (1)$57,464,250 100% $56,114,232 100% (1)  Includes foreign deposits of $474.3 million and $495.9 million at March 31, 2016 and December 31, 2015, respectively. |

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