| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (Lending Asset Quality Indicators) (Details) - USD ($) $ in Thousands** | Sep. 30, 2015 | Dec. 31, 2014 |
|-----------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | $ 39,824,202  | $ 36,640,761  |
| Pass                                                                                                            |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 37,963,785    | 35,042,081    |
| Special Mention                                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 888,927       | 655,721       |
| Substandard                                                                                                     |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 907,675       | 853,473       |
| Doubtful                                                                                                        |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 63,815        | 89,486        |
| Corporate banking                                                                                               |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 2,967,780     | 3,218,151     |
| Corporate banking | Pass                                                                                        |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 2,623,982     | 2,910,957     |
| Corporate banking | Special Mention                                                                             |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 118,536       | 83,122        |
| Corporate banking | Substandard                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 215,912       | 192,911       |
| Corporate banking | Doubtful                                                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 9,350         | 31,161        |
| Middle market commercial real estate                                                                            |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 3,965,173     | 3,743,100     |
| Middle market commercial real estate | Pass                                                                     |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 3,765,920     | 3,472,448     |
| Middle market commercial real estate | Special Mention                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 48,842        | 61,166        |
| Middle market commercial real estate | Substandard                                                              |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 127,213       | 174,882       |
| Middle market commercial real estate | Doubtful                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 23,198        | 34,604        |
| Santander real estate capital                                                                                   |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 1,562,229     | 1,777,982     |
| Santander real estate capital | Pass                                                                            |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 1,392,754     | 1,564,983     |
| Santander real estate capital | Special Mention                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 121,441       | 133,950       |
| Santander real estate capital | Substandard                                                                     |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 47,375        | 76,232        |
| Santander real estate capital | Doubtful                                                                        |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 659           | 2,817         |
| Commercial and industrial loans                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 19,361,751    | 17,111,406    |
| Commercial and industrial loans | Pass                                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 18,527,810    | 16,495,319    |
| Commercial and industrial loans | Special Mention                                                               |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 374,448       | 237,331       |
| Commercial and industrial loans | Substandard                                                                   |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 429,623       | 358,782       |
| Commercial and industrial loans | Doubtful                                                                      |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 29,870        | 19,974        |
| Multi-family                                                                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 9,600,527     | 8,705,890     |
| Multi-family | Pass                                                                                             |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 9,333,083     | 8,533,427     |
| Multi-family | Special Mention                                                                                  |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 195,710       | 131,677       |
| Multi-family | Substandard                                                                                      |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 71,301        | 40,355        |
| Multi-family | Doubtful                                                                                         |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 433           | 431           |
| Remaining commercial                                                                                            |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 2,366,742     | 2,084,232     |
| Remaining commercial | Pass                                                                                     |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 2,320,236     | 2,064,947     |
| Remaining commercial | Special Mention                                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 29,950        | 8,475         |
| Remaining commercial | Substandard                                                                              |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | 16,251        | 10,311        |
| Remaining commercial | Doubtful                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                      |          |          |
| Commercial loans                                                                                                | $ 305         | $ 499         |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Reflects the net carrying amount of commercial loans and leases held in portfolio, after deducting deferred income, but before deducting the allowance for losses on commercial loans and leases.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5074-111524
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