| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (As Restated) (Non-accrual Loans and Age Analysis of Past Due Loans) (Details) - USD ($) $ in Thousands** | Mar. 31, 2015 | Dec. 31, 2014 |
|---------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | $ 3,529,304   | $ 4,355,762   |
| Current                                                                                                                                           | 76,271,551    | 71,899,957    |
| Total Financing Receivables                                                                                                                       | 79,800,855    | 76,255,719    |
| Recorded Investment 90 Days and Accruing                                                                                                          | 84,567        | 93,152        |
| Corporate banking [Member]                                                                                                                        |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Financing Receivables                                                                                                                       | 3,170,416     | 3,218,150     |
| Middle market commercial real estate [Member]                                                                                                     |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Financing Receivables                                                                                                                       | 3,991,045     | 3,743,099     |
| Santander real estate capital [Member]                                                                                                            |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Financing Receivables                                                                                                                       | 1,638,296     | 1,777,984     |
| Commercial real estate loans [Member] | Corporate banking [Member]                                                                                |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 66,556        | 56,071        |
| Current                                                                                                                                           | 3,103,860     | 3,162,079     |
| Total Financing Receivables                                                                                                                       | 3,170,416     | 3,218,150     |
| Recorded Investment 90 Days and Accruing                                                                                                          | 0             | 0             |
| Commercial real estate loans [Member] | Middle market commercial real estate [Member]                                                             |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 27,487        | 36,783        |
| Current                                                                                                                                           | 3,963,558     | 3,706,316     |
| Total Financing Receivables                                                                                                                       | 3,991,045     | 3,743,099     |
| Recorded Investment 90 Days and Accruing                                                                                                          | 0             | 0             |
| Commercial real estate loans [Member] | Santander real estate capital [Member]                                                                    |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 2,925         | 6,444         |
| Current                                                                                                                                           | 1,635,371     | 1,771,540     |
| Total Financing Receivables                                                                                                                       | 1,638,296     | 1,777,984     |
| Recorded Investment 90 Days and Accruing                                                                                                          | 0             | 0             |
| Commercial and industrial loans [Member]                                                                                                          |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 59,127        | 50,212        |
| Current                                                                                                                                           | 18,775,248    | 17,061,710    |
| Total Financing Receivables                                                                                                                       | 18,834,375    | 17,111,922    |
| Recorded Investment 90 Days and Accruing                                                                                                          | 0             | 0             |
| Multi-family loans [Member]                                                                                                                       |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 11,259        | 19,322        |
| Current                                                                                                                                           | 8,541,652     | 8,686,568     |
| Total Financing Receivables                                                                                                                       | 8,552,911     | 8,705,890     |
| Recorded Investment 90 Days and Accruing                                                                                                          | 0             | 0             |
| Other commercial [Member]                                                                                                                         |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 6,881         | 6,299         |
| Current                                                                                                                                           | 2,141,399     | 2,077,933     |
| Total Financing Receivables                                                                                                                       | 2,148,280     | 2,084,232     |
| Recorded Investment 90 Days and Accruing                                                                                                          | 0             | 0             |
| Residential mortgages [Member]                                                                                                                    |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 326,370       | 366,088       |
| Current                                                                                                                                           | 6,687,906     | 6,603,221     |
| Total Financing Receivables                                                                                                                       | 7,014,276     | 6,969,309     |
| Recorded Investment 90 Days and Accruing                                                                                                          | 0             | 0             |
| Home equity loans and lines of credit [Member]                                                                                                    |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 118,934       | 122,823       |
| Current                                                                                                                                           | 6,057,365     | 6,088,475     |
| Total Financing Receivables                                                                                                                       | 6,176,299     | 6,211,298     |
| Recorded Investment 90 Days and Accruing                                                                                                          | 0             | 0             |
| Retail installment contracts and auto loans, originated [Member]                                                                                  |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 842,007       | 877,615       |
| Current                                                                                                                                           | 12,598,202    | 9,103,311     |
| Total Financing Receivables                                                                                                                       | 13,440,209    | 9,980,926     |
| Recorded Investment 90 Days and Accruing                                                                                                          | 0             | 0             |
| Retail installment contracts and auto loans, purchased [Member]                                                                                   |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 1,776,309     | 2,520,830     |
| Current                                                                                                                                           | 9,125,012     | 9,928,697     |
| Total Financing Receivables                                                                                                                       | 10,901,321    | 12,449,527    |
| Recorded Investment 90 Days and Accruing                                                                                                          | 0             | 0             |
| Personal unsecured loan [Member]                                                                                                                  |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 210,461       | 204,822       |
| Current                                                                                                                                           | 2,486,354     | 2,491,998     |
| Total Financing Receivables                                                                                                                       | 2,696,815     | 2,696,820     |
| Recorded Investment 90 Days and Accruing                                                                                                          | 84,567        | 93,152        |
| Other consumer [Member]                                                                                                                           |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 80,988        | 88,453        |
| Current                                                                                                                                           | 1,155,624     | 1,218,109     |
| Total Financing Receivables                                                                                                                       | 1,236,612     | 1,306,562     |
| Recorded Investment 90 Days and Accruing                                                                                                          | 0             | 0             |
| 30-89 Days Past Due                                                                                                                               |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 2,838,983     | 3,552,323     |
| 30-89 Days Past Due | Commercial real estate loans [Member] | Corporate banking [Member]                                                          |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 27,149        | 18,363        |
| 30-89 Days Past Due | Commercial real estate loans [Member] | Middle market commercial real estate [Member]                                       |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 1,224         | 3,179         |
| 30-89 Days Past Due | Commercial real estate loans [Member] | Santander real estate capital [Member]                                              |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 833           | 4,329         |
| 30-89 Days Past Due | Commercial and industrial loans [Member]                                                                                    |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 27,091        | 26,778        |
| 30-89 Days Past Due | Multi-family loans [Member]                                                                                                 |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 6,567         | 13,810        |
| 30-89 Days Past Due | Other commercial [Member]                                                                                                   |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 6,087         | 5,054         |
| 30-89 Days Past Due | Residential mortgages [Member]                                                                                              |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 144,471       | 165,270       |
| 30-89 Days Past Due | Home equity loans and lines of credit [Member]                                                                              |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 34,430        | 36,074        |
| 30-89 Days Past Due | Retail installment contracts and auto loans, originated [Member]                                                            |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 776,618       | 811,912       |
| 30-89 Days Past Due | Retail installment contracts and auto loans, purchased [Member]                                                             |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 1,658,261     | 2,317,941     |
| 30-89 Days Past Due | Personal unsecured loan [Member]                                                                                            |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 110,324       | 92,905        |
| 30-89 Days Past Due | Other consumer [Member]                                                                                                     |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 45,928        | 56,708        |
| Greater Than 90 Days                                                                                                                              |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 690,321       | 803,439       |
| Greater Than 90 Days | Commercial real estate loans [Member] | Corporate banking [Member]                                                         |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 39,407        | 37,708        |
| Greater Than 90 Days | Commercial real estate loans [Member] | Middle market commercial real estate [Member]                                      |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 26,263        | 33,604        |
| Greater Than 90 Days | Commercial real estate loans [Member] | Santander real estate capital [Member]                                             |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 2,092         | 2,115         |
| Greater Than 90 Days | Commercial and industrial loans [Member]                                                                                   |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 32,036        | 23,434        |
| Greater Than 90 Days | Multi-family loans [Member]                                                                                                |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 4,692         | 5,512         |
| Greater Than 90 Days | Other commercial [Member]                                                                                                  |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 794           | 1,245         |
| Greater Than 90 Days | Residential mortgages [Member]                                                                                             |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 181,899       | 200,818       |
| Greater Than 90 Days | Home equity loans and lines of credit [Member]                                                                             |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 84,504        | 86,749        |
| Greater Than 90 Days | Retail installment contracts and auto loans, originated [Member]                                                           |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 65,389        | 65,703        |
| Greater Than 90 Days | Retail installment contracts and auto loans, purchased [Member]                                                            |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 118,048       | 202,889       |
| Greater Than 90 Days | Personal unsecured loan [Member]                                                                                           |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | 100,137       | 111,917       |
| Greater Than 90 Days | Other consumer [Member]                                                                                                    |          |          |
| **Financing Receivable, Recorded Investments, Past Due [Line Items]**                                                                             |          |          |
| Total Past Due                                                                                                                                    | $ 35,060      | $ 31,745      |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Recorded investment in financing receivables that are 90 days or more past due and still accruing.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5111-111524
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Financing receivables that are current.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7A -URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953401-111524
+ Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentCurrent**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Recorded Investment in financing receivables that are past due at the balance sheet date.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 7A -URI http://asc.fasb.org/extlink&oid=49124121&loc=SL6953401-111524
+ Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentPastDue**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| 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_FinancingReceivableRecordedInvestmentPastDueLineItems**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                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_SantanderRealEstateCapitalMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_CommercialRealEstateLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_CommercialAndIndustrialLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_MultiFamilyCommercialLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=us-gaap_HomeEquityMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_RetailInstallmentContractsandAutoLoansOriginatedMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_RetailInstallmentContractsandAutoLoansPurchasedMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_PersonalUnsecuredLoanMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_OtherConsumerLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivablesPeriodPastDueAxis=sov_FinancingReceivables30to89DaysPastDueMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                       |
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