| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (As Restated) (Lending Asset Quality Indicators) (Details) - USD ($) $ in Thousands** | Mar. 31, 2015 | Dec. 31, 2014 |
|-------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | $ 79,800,855  | $ 76,255,719  |
| Commercial [Member]                                                                                                           |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 38,335,323    | 36,641,277    |
| Commercial [Member] | Pass [Member]                                                                                           |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 36,718,848    | 35,042,598    |
| Commercial [Member] | Special mention [Member]                                                                                |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 718,169       | 655,721       |
| Commercial [Member] | Substandard [Member]                                                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 813,226       | 853,473       |
| Commercial [Member] | Doubtful [Member]                                                                                       |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 85,080        | 89,485        |
| Corporate banking [Member]                                                                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 3,170,416     | 3,218,150     |
| Corporate banking [Member] | Pass [Member]                                                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 2,861,240     | 2,910,957     |
| Corporate banking [Member] | Special mention [Member]                                                                         |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 80,698        | 83,122        |
| Corporate banking [Member] | Substandard [Member]                                                                             |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 205,327       | 192,911       |
| Corporate banking [Member] | Doubtful [Member]                                                                                |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 23,151        | 31,160        |
| Middle market commercial real estate [Member]                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 3,991,045     | 3,743,099     |
| Middle market commercial real estate [Member] | Pass [Member]                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 3,734,456     | 3,472,448     |
| Middle market commercial real estate [Member] | Special mention [Member]                                                      |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 54,611        | 61,166        |
| Middle market commercial real estate [Member] | Substandard [Member]                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 172,695       | 174,882       |
| Middle market commercial real estate [Member] | Doubtful [Member]                                                             |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 29,283        | 34,603        |
| Santander real estate capital [Member]                                                                                        |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 1,638,296     | 1,777,984     |
| Santander real estate capital [Member] | Pass [Member]                                                                        |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 1,454,801     | 1,564,983     |
| Santander real estate capital [Member] | Special mention [Member]                                                             |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 121,364       | 133,950       |
| Santander real estate capital [Member] | Substandard [Member]                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 59,370        | 76,232        |
| Santander real estate capital [Member] | Doubtful [Member]                                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 2,761         | 2,819         |
| Commercial and industrial [Member]                                                                                            |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 18,834,375    | 17,111,922    |
| Commercial and industrial [Member] | Pass [Member]                                                                            |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 18,143,192    | 16,495,836    |
| Commercial and industrial [Member] | Special mention [Member]                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 339,161       | 237,331       |
| Commercial and industrial [Member] | Substandard [Member]                                                                     |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 323,465       | 358,782       |
| Commercial and industrial [Member] | Doubtful [Member]                                                                        |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 28,557        | 19,973        |
| Multi-family [Member]                                                                                                         |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 8,552,911     | 8,705,890     |
| Multi-family [Member] | Pass [Member]                                                                                         |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 8,393,127     | 8,533,427     |
| Multi-family [Member] | Special mention [Member]                                                                              |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 113,198       | 131,677       |
| Multi-family [Member] | Substandard [Member]                                                                                  |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 45,699        | 40,355        |
| Multi-family [Member] | Doubtful [Member]                                                                                     |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 887           | 431           |
| Remaining commercial [Member]                                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 2,148,280     | 2,084,232     |
| Remaining commercial [Member] | Pass [Member]                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 2,132,032     | 2,064,947     |
| Remaining commercial [Member] | Special mention [Member]                                                                      |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 9,137         | 8,475         |
| Remaining commercial [Member] | Substandard [Member]                                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 6,670         | 10,311        |
| Remaining commercial [Member] | Doubtful [Member]                                                                             |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 441           | 499           |
| Consumer [Member]                                                                                                             |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 41,465,532    | 39,614,442    |
| Consumer [Member] | Performing [Member]                                                                                       |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 40,387,918    | 38,222,276    |
| Consumer [Member] | Nonperforming [Member]                                                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 1,077,614     | 1,392,166     |
| Residential mortgages [Member]                                                                                                |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 7,014,276     | 6,969,309     |
| Residential mortgages [Member] | Performing [Member]                                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 6,802,154     | 6,737,993     |
| Residential mortgages [Member] | Nonperforming [Member]                                                                       |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 212,122       | 231,316       |
| Home equity loans and lines of credit [Member]                                                                                |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 6,176,299     | 6,211,298     |
| Home equity loans and lines of credit [Member] | Performing [Member]                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 6,035,978     | 6,069,272     |
| Home equity loans and lines of credit [Member] | Nonperforming [Member]                                                       |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 140,321       | 142,026       |
| Retail installment contracts and auto loans [Member]                                                                          |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 24,341,530    | 22,430,453    |
| Retail installment contracts and auto loans [Member] | Performing [Member]                                                    |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 23,651,485    | 21,447,731    |
| Retail installment contracts and auto loans [Member] | Nonperforming [Member]                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 690,045       | 982,722       |
| Personal unsecured loan [Member]                                                                                              |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 2,696,815     | 2,696,820     |
| Personal unsecured loan [Member] | Performing [Member]                                                                        |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 2,685,006     | 2,682,813     |
| Personal unsecured loan [Member] | Nonperforming [Member]                                                                     |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 11,809        | 14,007        |
| Other consumer [Member]                                                                                                       |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 1,236,612     | 1,306,562     |
| Other consumer [Member] | Performing [Member]                                                                                 |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | 1,213,295     | 1,284,467     |
| Other consumer [Member] | Nonperforming [Member]                                                                              |          |          |
| **Financing Receivable, Recorded Investment [Line Items]**                                                                    |          |          |
| Total loans                                                                                                                   | $ 23,317      | $ 22,095      |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
+ Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date. Such amount may include accrued interest receivable in accordance with the terms of the note. The note also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. Excludes amounts related to receivables held-for-sale.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.10(3)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878
+ Details**Name:**us-gaap_NotesReceivableGross**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=us-gaap_PassMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=us-gaap_SpecialMentionMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=us-gaap_SubstandardMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=us-gaap_DoubtfulMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_CorporateBankingCommercialLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_MiddleMarketCommercialRealEstateLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_SantanderRealEstateCapitalMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_CommercialAndIndustrialLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_MultiFamilyCommercialLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_OtherCommercialLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=us-gaap_PerformingFinancingReceivableMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=us-gaap_NonperformingFinancingReceivableMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_AutomobileLoanMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_PersonalUnsecuredLoanMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_OtherConsumerLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |