| **REGULATORY MATTERS (As Restated) (Tables)**                                         | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
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| **Banking and Thrift [Abstract]**                                                     |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
| Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations | The following schedule summarizes the actual capital balances of the Bank and SHUSA at December 31, 2015 and 2014:  REGULATORY CAPITAL  Common Equity Tier 1 Capital Ratio Tier 1 CapitalRatio Total CapitalRatio LeverageRatio ($ in thousands)Santander Bank at December 31, 2015(1):        Regulatory capital $9,857,655 $9,857,655 $10,775,851 $9,857,655Capital ratio 13.81% 13.81% 15.09% 11.46%SHUSA at December 31, 2015(1):        Regulatory capital $12,976,866 $14,676,251 $16,656,648 $14,676,251Capital ratio 11.97% 13.54% 15.37% 11.58%           Tier 1 Common Capital Tier 1 CapitalRatio Total CapitalRatio LeverageRatio  ($ in thousands)Santander Bank at December 31, 2014(2):        Regulatory capital $8,831,156 $8,831,156 $9,872,603 $8,831,156Capital ratio 13.23% 13.23% 14.79% 12.01%SHUSA at December 31, 2014(2):        Regulatory capital $10,962,078 $13,041,969 $15,056,913 $13,041,969Capital ratio 10.90% 12.96% 14.97% 12.27%(1)  Represents phase-in ratios under Basel III(2)  Represents ratios under Basel I |

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| - Definition
Tabular disclosure of the capital amounts and ratios as of the balance sheet date, indicating whether the entity or entities are in compliance with regulatory capital requirements, by entity.
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