| **INTERMEDIATE HOLDING COMPANY**  | 6 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
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| **Banking and Thrift [Abstract]** |                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
| INTERMEDIATE HOLDING COMPANY      | NOTE 18. INTERMEDIATE HOLDING COMPANYOn February 18, 2014, the Federal Reserve issued the final rule to strengthen regulatory oversight of FBOs (the “Final Rule”).  Under the Final Rule, FBOs with over $50 billion of U.S. non-branch assets, including Santander, were required to consolidate U.S. subsidiary activities under an Intermediate Holding Company ("IHC"). Due its U.S. non-branch total consolidated asset size, Santander was subject to the Final Rule. As a result of this rule, Santander transferred substantially all of its U.S. bank and non-bank subsidiaries previously outside the Company to the Company, which became an IHC effective July 1, 2016. These subsidiaries include Santander BanCorp, a Puerto Rico bank holding company, Banco Santander International, a private bank headquartered in Miami, Santander Investment Securities, Inc., a broker-dealer located in New York, and Santander Securities LLC, a Puerto Rico broker-dealer. As these entities were and are solely owned and controlled by Santander prior to and after July 1, 2016, in accordance with ASC 805, the transaction has been accounted for under the common control guidance which requires the Company to recognize the assets and liabilities transferred at their historical cost of the transferring entity at the date of the transfer. The entities transferred approximately $14.1 billion of assets and approximately $11.8 billion of liabilities to the Company. Since the entities were all under common control, the transferred approximately $46.9 million of net income to the Company for the six-month period ended June 30, 2016 after the financial statements have been recast to reflect the operations of the commonly controlled entities for all periods presented as a change in reporting entity. |

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The entire disclosure for financial services specifically banking and thrift entities at the end of the reporting period.
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