| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (As Restated) (Portfolio Segments and Classes) (Details) - USD ($) $ in Thousands**                                                                                                                                                                                                                                                                                                                                                                             | Mar. 31, 2015 | Dec. 31, 2014 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | $ 79,800,855  | $ 76,255,719 |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | [1],[2]       | 78,438,960    | 75,995,467 |
| Commercial and industrial loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 18,834,375    | 17,111,922 |
| Multi-family loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 8,552,911     | 8,705,890 |
| Other commercial [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 2,148,280     | 2,084,232 |
| Residential mortgages [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 7,014,276     | 6,969,309 |
| Home equity loans and lines of credit [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                          |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 6,176,299     | 6,211,298 |
| Retail installment contracts and auto loans, originated [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                        |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 13,440,209    | 9,980,926 |
| Retail installment contracts and auto loans, purchased [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                         |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 10,901,321    | 12,449,527 |
| Personal unsecured loan [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 2,696,815     | 2,696,820 |
| Corporate banking [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 3,170,416     | 3,218,150 |
| Corporate banking [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                      |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 3,170,416     | 3,218,150 |
| Middle market commercial real estate [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 3,991,045     | 3,743,099 |
| Middle market commercial real estate [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                   |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 3,991,045     | 3,743,099 |
| Santander real estate capital [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 1,638,296     | 1,777,984 |
| Santander real estate capital [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                          |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 1,638,296     | 1,777,984 |
| Consumer loans secured by real estate [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                          |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               | 12,892,481    | 12,984,873 |
| Consumer loans secured by real estate [Member] | Residential mortgages [Member]                                                                                                                                                                                                                                                                                                                                                                                                                         |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               | 6,716,182     | 6,773,575 |
| Consumer loans secured by real estate [Member] | Home equity loans and lines of credit [Member]                                                                                                                                                                                                                                                                                                                                                                                                         |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               | 6,176,299     | 6,211,298 |
| Consumer loans not secured by real estate [Member] | Retail installment contracts and auto loans, originated [Member]                                                                                                                                                                                                                                                                                                                                                                                   |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               | 12,420,733    | 9,935,503 |
| Consumer loans not secured by real estate [Member] | Retail installment contracts and auto loans, purchased [Member]                                                                                                                                                                                                                                                                                                                                                                                    |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               | 10,901,321    | 12,449,526 |
| Consumer loans not secured by real estate [Member] | Personal unsecured loan [Member]                                                                                                                                                                                                                                                                                                                                                                                                                   |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               | 2,696,815     | 2,696,820 |
| Consumer loans not secured by real estate [Member] | Other consumer [Member]                                                                                                                                                                                                                                                                                                                                                                                                                            |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               | 1,236,612     | 1,306,562 |
| Commercial Portfolio Segment [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 38,290,998    | 36,622,183 |
| Commercial Portfolio Segment [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 8,799,757     | 8,739,233 |
| Commercial Portfolio Segment [Member] | Commercial and industrial loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                        |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 18,790,050    | 17,092,828 |
| Loans held-for-sale                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |               | 44,300        | 19,100 |
| Commercial Portfolio Segment [Member] | Multi-family loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                     |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 8,552,911     | 8,705,890 |
| Commercial Portfolio Segment [Member] | Other commercial [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 2,148,280     | 2,084,232 |
| Commercial Portfolio Segment [Member] | Corporate banking [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                                              |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 3,170,416     | 3,218,150 |
| Commercial Portfolio Segment [Member] | Middle market commercial real estate [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 3,991,045     | 3,743,099 |
| Commercial Portfolio Segment [Member] | Santander real estate capital [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                                  |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 1,638,296     | 1,777,984 |
| Other consumer [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 40,147,962    | 39,373,284 |
| Other consumer [Member] | Residential mortgages [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held-for-sale                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |               | 298,100       | 195,700 |
| Other consumer [Member] | Retail installment contracts and auto loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                          |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held-for-sale                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |               | 1,000,000     | 45,400 |
| Other consumer [Member] | Consumer loans secured by real estate [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | 12,892,481    | 12,984,873 |
| Other consumer [Member] | Consumer loans secured by real estate [Member] | Residential mortgages [Member]                                                                                                                                                                                                                                                                                                                                                                                               |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               | 6,716,182     | 6,773,575 |
| Other consumer [Member] | Consumer loans secured by real estate [Member] | Home equity loans and lines of credit [Member]                                                                                                                                                                                                                                                                                                                                                                               |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               | 6,176,299     | 6,211,298 |
| Other consumer [Member] | Consumer loans not secured by real estate [Member] | Retail installment contracts and auto loans, originated [Member]                                                                                                                                                                                                                                                                                                                                                         |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               | 12,420,733    | 9,935,503 |
| Other consumer [Member] | Consumer loans not secured by real estate [Member] | Retail installment contracts and auto loans, purchased [Member]                                                                                                                                                                                                                                                                                                                                                          |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               |          | 12,449,526 |
| Other consumer [Member] | Consumer loans not secured by real estate [Member] | Personal unsecured loan [Member]                                                                                                                                                                                                                                                                                                                                                                                         |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               | 2,696,815     | 2,696,820 |
| Other consumer [Member] | Consumer loans not secured by real estate [Member] | Other consumer [Member]                                                                                                                                                                                                                                                                                                                                                                                                  |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               | $ 1,236,612   | $ 1,306,562 |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
| [1]Loans held for investment includes $676.1 million and $845.9 million of loans recorded at fair value at March 31, 2015 and December 31, 2014, respectively.[2]The Company has interests in certain securitization trusts ("Trusts") that are considered variable interest entities ("VIEs") for accounting purposes. The Company consolidates VIEs where it is deemed the primary beneficiary. See Note 7 to these Condensed Consolidated Financial Statements for additional information. |

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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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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| - Definition
Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522Reference 2: 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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| - Definition
Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.
+ References
No definition available.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date. Such amount may include accrued interest receivable in accordance with the terms of the note. The note also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. Excludes amounts related to receivables held-for-sale.
+ References
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