| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (As Restated) (Non-accrual Loans) (Details) - USD ($) $ in Thousands** | Sep. 30, 2015 | Dec. 31, 2014 |
|----------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | $ 1,486,630   | $ 1,628,288   |
| Foreclosed and other repossessed assets                                                                        | 154,434       | 136,305       |
| Nonperforming                                                                                                  |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Other real estate owned (OREO)                                                                                 | 40,692        | 65,051        |
| Repossessed vehicles                                                                                           | 154,057       | 126,309       |
| Foreclosed and other repossessed assets                                                                        | 377           | 11,375        |
| Total OREO and other repossessed assets                                                                        | 195,126       | 202,735       |
| Total non-performing assets                                                                                    | 1,681,756     | 1,831,023     |
| Commercial                                                                                                     |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 180,145       | 236,122       |
| Consumer                                                                                                       |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 1,306,485     | 1,392,166     |
| Corporate banking                                                                                              |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 60,450        | 90,579        |
| Middle market commercial real estate                                                                           |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 38,605        | 71,398        |
| Santander real estate capital                                                                                  |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 3,505         | 5,803         |
| Commercial and industrial                                                                                      |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 65,901        | 54,567        |
| Multi-family                                                                                                   |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 7,319         | 9,639         |
| Other commercial                                                                                               |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 4,365         | 4,136         |
| Residential mortgages                                                                                          |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 184,828       | 231,316       |
| Home equity loans and lines of credit                                                                          |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 126,628       | 142,026       |
| Retail installment contracts and auto loans, originated                                                        |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 538,929       | 227,132       |
| Retail installment contracts and auto loans, purchased                                                         |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 412,175       | 755,590       |
| Personal unsecured loans                                                                                       |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | 12,683        | 14,007        |
| Other consumer                                                                                                 |          |          |
| **Financing Receivable, Recorded Investment, Past Due [Line Items]**                                           |          |          |
| Non-accrual loans                                                                                              | $ 31,242      | $ 22,095      |

| X                                                                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Repossessed Vehicles
+ References
No definition available.
+ Details**Name:**sov_RepossessedVehicles**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Recorded investment in financing receivables that are on nonaccrual status as of 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 7 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5111-111524
+ Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentNonaccrualStatus**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
Carrying amount as of the balance sheet date of all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance; includes real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4437-111522Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5162-111524
+ Details**Name:**us-gaap_ForeclosedAssets**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Reflects the carrying amount of loans deemed to be questionable as to collection on which no interest is continuing to be recognized.
+ 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 (a) -URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5111-111524
+ Details**Name:**us-gaap_LoansAndLeasesReceivableImpairedNonperformingNonaccrualOfInterest**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Carrying amount as of the balance sheet date of assets other than real property that were received in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5162-111524Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4437-111522
+ Details**Name:**us-gaap_OtherForeclosedAssets**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=49124121&loc=d3e5162-111524Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4437-111522Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 28 -Article 12Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph c -Subparagraph Schedule III -Article 5
+ Details**Name:**us-gaap_RealEstateAcquiredThroughForeclosure**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=us-gaap_NonperformingFinancingReceivableMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**sov_LoanTypeAxis=us-gaap_CommercialPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**sov_LoanTypeAxis=us-gaap_ConsumerPortfolioSegmentMember**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_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=sov_RetailInstallmentContractsandAutoLoansOriginatedMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_RetailInstallmentContractsandAutoLoansPurchasedMember**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:** |