| **EQUITY METHOD INVESTMENTS AND VARIABLE INTEREST ENTITIES (Schedule of VIEs) (Details) (USD $)In Thousands, unless otherwise specified** | Dec. 31, 2014                                                                                                                                                                                    | Dec. 31, 2013                                                                                                                                                                                    |
|-------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| **Variable Interest Entity [Line Items]**                                                                                                 |                                                                                                                                                                                             |                                                                                                                                                                                             |
| Maximum Exposure, Investment in Equity                                                                                                    | $ 55,313us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssetsAndLiabilitiesNet                                                                                                       | $ 73,445us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssetsAndLiabilitiesNet                                                                                                       |
| Maximum Exposure, Commitments                                                                                                             | 0us-gaap_VariableInterestDifferenceBetweenCarryingAmountAndMaximumExposure                                                                                                                       | 141us-gaap_VariableInterestDifferenceBetweenCarryingAmountAndMaximumExposure                                                                                                                     |
| Total                                                                                                                                     | 55,313us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount                                                                                                                              | 73,586us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount                                                                                                                              |
| Low Income Housing Partnerships [Member]                                                                                                  |                                                                                                                                                                                             |                                                                                                                                                                                             |
| **Variable Interest Entity [Line Items]**                                                                                                 |                                                                                                                                                                                             |                                                                                                                                                                                             |
| Maximum Exposure, Investment in Equity                                                                                                    | 18,815us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssetsAndLiabilitiesNet/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis= sov_LowIncomeHousingPartnershipsMember   | 34,374us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssetsAndLiabilitiesNet/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis= sov_LowIncomeHousingPartnershipsMember   |
| Maximum Exposure, Commitments                                                                                                             | 0us-gaap_VariableInterestDifferenceBetweenCarryingAmountAndMaximumExposure/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis= sov_LowIncomeHousingPartnershipsMember                 | 141us-gaap_VariableInterestDifferenceBetweenCarryingAmountAndMaximumExposure/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis= sov_LowIncomeHousingPartnershipsMember               |
| Total                                                                                                                                     | 18,815us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis= sov_LowIncomeHousingPartnershipsMember                        | 34,515us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis= sov_LowIncomeHousingPartnershipsMember                        |
| New Market Partnerships [Member]                                                                                                          |                                                                                                                                                                                             |                                                                                                                                                                                             |
| **Variable Interest Entity [Line Items]**                                                                                                 |                                                                                                                                                                                             |                                                                                                                                                                                             |
| Maximum Exposure, Investment in Equity                                                                                                    | 36,498us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssetsAndLiabilitiesNet/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis= sov_NewMarketTaxCreditPartnershipsMember | 39,071us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssetsAndLiabilitiesNet/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis= sov_NewMarketTaxCreditPartnershipsMember |
| Maximum Exposure, Commitments                                                                                                             | 0us-gaap_VariableInterestDifferenceBetweenCarryingAmountAndMaximumExposure/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis= sov_NewMarketTaxCreditPartnershipsMember               | 0us-gaap_VariableInterestDifferenceBetweenCarryingAmountAndMaximumExposure/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis= sov_NewMarketTaxCreditPartnershipsMember               |
| Total                                                                                                                                     | $ 36,498us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis= sov_NewMarketTaxCreditPartnershipsMember                    | $ 39,071us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount/ us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis= sov_NewMarketTaxCreditPartnershipsMember                    |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Difference between the carrying amount of assets and liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the variable interest entity (VIE) and the reporting entity's maximum exposure to loss as a result of its involvement with the VIE, where the reporting entity is not the VIE's primary beneficiary.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5728-111685
+ Details**Name:**us-gaap_VariableInterestDifferenceBetweenCarryingAmountAndMaximumExposure**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph b -URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5728-111685Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=28200181&loc=d3e5747-111685
+ Details**Name:**us-gaap_VariableInterestEntityEntityMaximumLossExposureAmount**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_VariableInterestEntityLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Net carrying amount of the assets and liabilities in the reporting entity's statement of financial position that relate to the reporting entity's variable interest in the Variable Interest Entity (VIE), when the reporting entity is not the VIE's primary beneficiary.
+ References
No definition available.
+ Details**Name:**us-gaap_VariableInterestEntityNonconsolidatedCarryingAmountAssetsAndLiabilitiesNet**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=sov_LowIncomeHousingPartnershipsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_VariableInterestEntitiesByClassificationOfEntityAxis=sov_NewMarketTaxCreditPartnershipsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |