| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (As Restated) (Non-accrual Loans) (Details) - USD ($) $ in Thousands** | Dec. 31, 2015 | Dec. 31, 2014 |
|----------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | $ 1,655,099   | $ 1,628,288   |
| Foreclosed and other repossessed assets                                                                        | 172,749       | 136,305       |
| Nonperforming                                                                                                  |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Other real estate owned (OREO)                                                                                 | 38,959        | 65,051        |
| Repossessed vehicles                                                                                           | 172,375       | 126,309       |
| Foreclosed and other repossessed assets                                                                        | 374           | 11,375        |
| Total OREO and other repossessed assets                                                                        | 211,708       | 202,735       |
| Total non-performing assets                                                                                    | 1,866,807     | 1,831,023     |
| Commercial                                                                                                     |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 211,067       | 236,122       |
| Commercial | Corporate banking                                                                                 |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 71,979        | 90,579        |
| Commercial | Middle market commercial real estate                                                              |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 37,745        | 71,398        |
| Commercial | Santander real estate capital                                                                     |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 3,454         | 5,803         |
| Commercial | Commercial and industrial                                                                         |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 85,745        | 54,567        |
| Commercial | Multifamily                                                                                       |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 9,162         | 9,639         |
| Commercial | Other commercial                                                                                  |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 2,982         | 4,136         |
| Consumer                                                                                                       |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 1,444,032     | 1,392,166     |
| Consumer | Residential mortgages                                                                               |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 173,780       | 231,316       |
| Consumer | Home equity loans and lines of credit                                                               |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 127,171       | 142,026       |
| Consumer | Retail installment contracts and auto loans, originated                                             |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 701,785       | 227,132       |
| Consumer | Retail installment contracts and auto loans, purchased                                              |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 417,276       | 755,590       |
| Consumer | Personal unsecured loans                                                                            |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 895           | 14,007        |
| Consumer | Other consumer                                                                                      |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | $ 23,125      | $ 22,095      |

| X                                                                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Repossessed Vehicles
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.
+ References
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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.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Carrying amount as of the balance sheet date of all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance; includes real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Reflects the carrying amount of loans deemed to be questionable as to collection on which no interest is continuing to be recognized.
+ References
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| - Definition
Carrying amount as of the balance sheet date of assets other than real property that were received in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance.
+ References
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.
+ References
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