| **REGULATORY MATTERS (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 Basel I capital balances of the Bank and SHUSA at December 31, 2014 and 2013:  REGULATORY CAPITAL  Tier 1 LeverageCapital Ratio Tier 1 Risk-BasedCapital Ratio Total Risk-BasedCapital Ratio Tier 1 Common Capital Ratio(1) ($ in thousands)Santander Bank at December 31, 2014:        Regulatory capital $8,831,156 $8,831,156 $9,872,603 $8,831,156Capital ratio 12.01% 13.23% 14.79% 13.23%SHUSA at December 31, 2014 (2):        Regulatory capital $12,897,342 $12,897,342 $14,847,924 $10,853,488Capital ratio 12.18% 12.87% 14.82% 10.83%Santander Bank at December 31, 2013:        Regulatory capital $8,390,428 $8,390,428 $9,550,558 $8,390,428Capital ratio 12.09% 13.96% 15.89% 13.96%SHUSA at December 31, 2013 (3):        Regulatory capital $9,210,100 $9,210,100 $10,555,146 $8,794,393Capital ratio 12.78% 14.67% 16.81% 14.01%(1)Ratio presented due to regulators emphasizing the Tier 1 common capital ratio in their evaluation of bank and BHC capital levels, although this metric is not provided for in bank regulations. For all BHCs undergoing its CCAR, the FRB has established a 5% minimum Tier 1 common capital ratio under stress scenarios.(2)Ratios reflect the reconsolidation of SCUSA, following the Change in Control.(3)Ratios have been determined using SHUSA's accounting method for SCUSA as an equity method investment, prior to the Change in Control. |

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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.
+ References
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