| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (Lending Asset Quality Indicators) (Details) - USD ($) $ in Thousands** | Jun. 30, 2016 | Dec. 31, 2015 |
|-----------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | $ 41,564,581  | $ 40,712,119  |
| Pass                                                                                                            |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 39,462,987    | 38,673,364    |
| Special Mention                                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 950,532       | 1,043,286     |
| Substandard                                                                                                     |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 1,058,732     | 926,537       |
| Doubtful                                                                                                        |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 92,330        | 68,932        |
| Commercial and industrial loans                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 20,079,491    | 19,874,233    |
| Commercial and industrial loans | Pass                                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 18,780,657    | 18,881,150    |
| Commercial and industrial loans | Special Mention                                                               |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 581,885       | 492,128       |
| Commercial and industrial loans | Substandard                                                                   |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 684,355       | 467,983       |
| Commercial and industrial loans | Doubtful                                                                      |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 32,594        | 32,972        |
| Multifamily                                                                                                     |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 9,225,985     | 9,438,463     |
| Multifamily | Pass                                                                                              |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 9,066,369     | 9,114,466     |
| Multifamily | Special Mention                                                                                   |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 102,972       | 249,165       |
| Multifamily | Substandard                                                                                       |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 56,244        | 74,410        |
| Multifamily | Doubtful                                                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 400           | 422           |
| Remaining commercial                                                                                            |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 3,006,362     | 2,676,506     |
| Remaining commercial | Pass                                                                                     |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 2,974,771     | 2,631,935     |
| Remaining commercial | Special Mention                                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 11,904        | 28,686        |
| Remaining commercial | Substandard                                                                              |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 19,460        | 15,601        |
| Remaining commercial | Doubtful                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 227           | 284           |
| Commercial | Corporate banking                                                                                  |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 2,885,532     | 2,949,089     |
| Commercial | Corporate banking | Pass                                                                           |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 2,638,995     | 2,627,159     |
| Commercial | Corporate banking | Special Mention                                                                |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 76,248        | 99,090        |
| Commercial | Corporate banking | Substandard                                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 160,420       | 208,785       |
| Commercial | Corporate banking | Doubtful                                                                       |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 9,869         | 14,055        |
| Commercial | Middle market commercial real estate                                                               |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 4,872,407     | 4,223,359     |
| Commercial | Middle market commercial real estate | Pass                                                        |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 4,610,178     | 4,055,623     |
| Commercial | Middle market commercial real estate | Special Mention                                             |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 102,358       | 29,620        |
| Commercial | Middle market commercial real estate | Substandard                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 110,631       | 117,571       |
| Commercial | Middle market commercial real estate | Doubtful                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 49,240        | 20,545        |
| Commercial | Santander real estate capital                                                                      |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 1,494,804     | 1,550,469     |
| Commercial | Santander real estate capital | Pass                                                               |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 1,392,017     | 1,363,031     |
| Commercial | Santander real estate capital | Special Mention                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 75,165        | 144,597       |
| Commercial | Santander real estate capital | Substandard                                                        |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 27,622        | 42,187        |
| Commercial | Santander real estate capital | Doubtful                                                           |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | $ 0           | $ 654         |

| X                                                                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans and Leases Receivable, Including Held-for-Sale, Commercial, Net of Deferred Income
+ References
No definition available.
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No definition available.
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