| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (As Restated) (Non-performing Assets) (Details) - USD ($) $ in Thousands** | Mar. 31, 2015 | Dec. 31, 2014 | Mar. 31, 2014 |
|--------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | $ 1,310,062   | $ 1,628,288   |          |
| Other repossessed assets                                                                                           | 160,151       | 136,305       |          |
| Total non-performing assets                                                                                        | 123,416,531   | 118,820,880   | $ 109,202,366 |
| Nonperforming [Member]                                                                                             |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Other real estate owned                                                                                            | 52,157        | 65,051        |          |
| Repossessed vehicles                                                                                               | 159,990       | 126,309       |          |
| Other repossessed assets                                                                                           | 161           | 11,375        |          |
| Total other real estate owned and other repossessed assets                                                         | 212,308       | 202,735       |          |
| Total non-performing assets                                                                                        | 1,522,370     | 1,831,023     |          |
| Commercial [Member]                                                                                                |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | 232,448       | 236,122       |          |
| Consumer [Member]                                                                                                  |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | 1,077,614     | 1,392,166     |          |
| Commercial real estate loans [Member] | Corporate banking [Member]                                                 |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | 87,671        | 90,579        |          |
| Commercial real estate loans [Member] | Middle market commercial real estate [Member]                              |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | 59,936        | 71,398        |          |
| Commercial real estate loans [Member] | Santander real estate capital [Member]                                     |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | 5,697         | 5,803         |          |
| Commercial and industrial loans [Member]                                                                           |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | 65,952        | 54,567        |          |
| Multi-family loans [Member]                                                                                        |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | 9,746         | 9,639         |          |
| Other commercial [Member]                                                                                          |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | 3,446         | 4,136         |          |
| Residential mortgages [Member]                                                                                     |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | 212,122       | 231,316       |          |
| Home equity loans and lines of credit [Member]                                                                     |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | 140,321       | 142,026       |          |
| Retail installment contracts and auto loans, originated [Member]                                                   |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | 217,500       | 227,132       |          |
| Retail installment contracts and auto loans, purchased [Member]                                                    |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | 472,545       | 755,590       |          |
| Personal unsecured loan [Member]                                                                                   |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | 11,809        | 14,007        |          |
| Other consumer [Member]                                                                                            |          |          |          |
| **Nonperforming Assets [Line Items]**                                                                              |          |          |          |
| Non-accrual loans                                                                                                  | $ 23,317      | $ 22,095      |          |

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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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Nonperforming assets.
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| - Definition
Repossessed Vehicles
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.
+ References
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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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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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
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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