| **BUSINESS COMBINATIONS (Gain in Change in Control) (Details) (USD $)** | 3 Months Ended                               | 0 Months Ended                                           |
|-------------------------------------------------------------------------|----------------------------------------------|----------------------------------------------------------|
||
| **Business Acquisition [Line Items]**                                   |                                         |                                                     |   |
| Gain attributable to SCUSA shares sold                                  | $ 0us-gaap_GainLossOnSaleOfEquityInvestments | $ (320,145,000)us-gaap_GainLossOnSaleOfEquityInvestments |   |
| SCUSA [Member]                                                          |                                         |                                                     |   |
| **Business Acquisition [Line Items]**                                   |                                         |                                                     |   |
| Gain attributable to SCUSA shares sold                                  |                                         |                                                     | 137,536,000us-gaap_GainLossOnSaleOfEquityInvestments/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember |
| Gain attributable to the remaining equity interest                      |                                         |                                                     | 2,291,003,000sov_BusinessCombinationGainRecognizedAmountAttributabletoAcquireeSharesSold/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember |
| Total pre-tax gain                                                      |                                         |                                                     | 2,428,539,000us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember |
| Number of shares issued                                                 |                                         |                                                     | 13,895,243us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember |
| Proceeds from sale of SCUSA common stock                                |                                         |                                                     | $ 320,100,000us-gaap_EquityMethodInvestmentNetSalesProceeds/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember |

| X                                                                                                                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Business Combination, Gain Recognized, Amount Attributable to Acquiree Shares Sold
+ References
No definition available.
+ Details**Name:**sov_BusinessCombinationGainRecognizedAmountAttributabletoAcquireeSharesSold**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_BusinessAcquisitionLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
In a business combination achieved in stages, this element represents the amount of gain recognized by the entity as a result of remeasuring to fair value the equity interest in the acquiree it held before the business combination.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g)(2) -URI http://asc.fasb.org/extlink&oid=25497992&loc=d3e1392-128463
+ Details**Name:**us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeRemeasurementGain**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the amount of net sales proceeds received on disposal of an equity method investment.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 35 -Paragraph 35 -URI http://asc.fasb.org/extlink&oid=35687916&loc=d3e32847-111569
+ Details**Name:**us-gaap_EquityMethodInvestmentNetSalesProceeds**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The difference between the carrying value and the sale price of equity securities, not separately or otherwise categorized as trading or available-for-sale. This element includes investments in which the entity holds a small ownership stake (generally, less than 20% of the shares outstanding) and cannot exert significant influence.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.13(h)) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882
+ Details**Name:**us-gaap_GainLossOnSaleOfEquityInvestments**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The number of shares issued or sold by the subsidiary or equity method investee per stock transaction.
+ References
No definition available.
+ Details**Name:**us-gaap_SaleOfStockNumberOfSharesIssuedInTransaction**Namespace Prefix:**us-gaap_**Data Type:**xbrli:sharesItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_BusinessAcquisitionAxis=sov_ScusaMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |