| **DERIVATIVES (Income Statement Effect) (Details) (USD $)In Thousands, unless otherwise specified** | 3 Months Ended                                                                                                                                                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| Cross currency swaps [Member] | Miscellaneous income [Member] | Fair value hedges [Member]          |                                                                                                                                                                                                                                                                                       |   |
| **Derivative Instruments, Gain (Loss) [Line Items]**                                                |                                                                                                                                                                                                                                                                                       |   |
| Gain (loss) recognized on all derivatives                                                           | $ (36)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_CurrencySwapMember/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis= us-gaap_FairValueHedgingMember/ us-gaap_IncomeStatementLocationAxis= sov_MiscellaneousIncomeMember      | $ (681)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_CurrencySwapMember/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis= us-gaap_FairValueHedgingMember/ us-gaap_IncomeStatementLocationAxis= sov_MiscellaneousIncomeMember |
| Interest rate swaps [Member] | Miscellaneous income [Member] | Fair value hedges [Member]           |                                                                                                                                                                                                                                                                                       |   |
| **Derivative Instruments, Gain (Loss) [Line Items]**                                                |                                                                                                                                                                                                                                                                                       |   |
| Gain (loss) recognized on all derivatives                                                           | (2,993)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateSwapMember/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis= us-gaap_FairValueHedgingMember/ us-gaap_IncomeStatementLocationAxis= sov_MiscellaneousIncomeMember | 735us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateSwapMember/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis= us-gaap_FairValueHedgingMember/ us-gaap_IncomeStatementLocationAxis= sov_MiscellaneousIncomeMember |
| Interest rate swaps [Member] | Net interest income [Member] | Cash flow hedges [Member]             |                                                                                                                                                                                                                                                                                       |   |
| **Derivative Instruments, Gain (Loss) [Line Items]**                                                |                                                                                                                                                                                                                                                                                       |   |
| Gain (loss) recognized on all derivatives                                                           | (4,451)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateSwapMember/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis= us-gaap_CashFlowHedgingMember/ us-gaap_IncomeStatementLocationAxis= sov_NetInterestIncomeMember    | (13,685)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateSwapMember/ us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis= us-gaap_CashFlowHedgingMember/ us-gaap_IncomeStatementLocationAxis= sov_NetInterestIncomeMember |
| Forward commitments to sell loans [Member] | Mortgage banking income [Member]                       |                                                                                                                                                                                                                                                                                       |   |
| **Derivative Instruments, Gain (Loss) [Line Items]**                                                |                                                                                                                                                                                                                                                                                       |   |
| Gain (loss) recognized on all derivatives                                                           | (187)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= sov_ForwardCommitmentsToSellLoansMember/ us-gaap_IncomeStatementLocationAxis= sov_MortgageBankingIncomeMember                                                                                        | (2,009)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= sov_ForwardCommitmentsToSellLoansMember/ us-gaap_IncomeStatementLocationAxis= sov_MortgageBankingIncomeMember |
| Interest rate lock commitments [Member] | Mortgage banking income [Member]                          |                                                                                                                                                                                                                                                                                       |   |
| **Derivative Instruments, Gain (Loss) [Line Items]**                                                |                                                                                                                                                                                                                                                                                       |   |
| Gain (loss) recognized on all derivatives                                                           | 3,937us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateLockCommitmentsMember/ us-gaap_IncomeStatementLocationAxis= sov_MortgageBankingIncomeMember                                                                                      | 1,181us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateLockCommitmentsMember/ us-gaap_IncomeStatementLocationAxis= sov_MortgageBankingIncomeMember |
| Mortgage servicing rghts [Member] | Mortgage banking income [Member]                                |                                                                                                                                                                                                                                                                                       |   |
| **Derivative Instruments, Gain (Loss) [Line Items]**                                                |                                                                                                                                                                                                                                                                                       |   |
| Gain (loss) recognized on all derivatives                                                           | (1,219)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= sov_MortgageServicingRightsMember/ us-gaap_IncomeStatementLocationAxis= sov_MortgageBankingIncomeMember                                                                                            | (7,761)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= sov_MortgageServicingRightsMember/ us-gaap_IncomeStatementLocationAxis= sov_MortgageBankingIncomeMember |
| Customer related derivatives [Member] | Miscellaneous income [Member]                               |                                                                                                                                                                                                                                                                                       |   |
| **Derivative Instruments, Gain (Loss) [Line Items]**                                                |                                                                                                                                                                                                                                                                                       |   |
| Gain (loss) recognized on all derivatives                                                           | 418us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= sov_CustomerRelatedDerivativesMember/ us-gaap_IncomeStatementLocationAxis= sov_MiscellaneousIncomeMember                                                                                               | 113us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= sov_CustomerRelatedDerivativesMember/ us-gaap_IncomeStatementLocationAxis= sov_MiscellaneousIncomeMember |
| Foreign exchange [Member] | Miscellaneous income [Member]                                           |                                                                                                                                                                                                                                                                                       |   |
| **Derivative Instruments, Gain (Loss) [Line Items]**                                                |                                                                                                                                                                                                                                                                                       |   |
| Gain (loss) recognized on all derivatives                                                           | (874)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_ForeignExchangeContractMember/ us-gaap_IncomeStatementLocationAxis= sov_MiscellaneousIncomeMember                                                                                            | (911)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_ForeignExchangeContractMember/ us-gaap_IncomeStatementLocationAxis= sov_MiscellaneousIncomeMember |
| SCUSA derivatives [Member] | Miscellaneous income [Member]                                          |                                                                                                                                                                                                                                                                                       |   |
| **Derivative Instruments, Gain (Loss) [Line Items]**                                                |                                                                                                                                                                                                                                                                                       |   |
| Gain (loss) recognized on all derivatives                                                           | (2,397)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= sov_SCUSADerivativesMember/ us-gaap_IncomeStatementLocationAxis= sov_MiscellaneousIncomeMember                                                                                                     | 13,025us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= sov_SCUSADerivativesMember/ us-gaap_IncomeStatementLocationAxis= sov_MiscellaneousIncomeMember |
| SCUSA derivatives [Member] | Net interest income [Member]                                           |                                                                                                                                                                                                                                                                                       |   |
| **Derivative Instruments, Gain (Loss) [Line Items]**                                                |                                                                                                                                                                                                                                                                                       |   |
| Gain (loss) recognized on all derivatives                                                           | 18,044us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= sov_SCUSADerivativesMember/ us-gaap_IncomeStatementLocationAxis= sov_NetInterestIncomeMember                                                                                                        | (1,839)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= sov_SCUSADerivativesMember/ us-gaap_IncomeStatementLocationAxis= sov_NetInterestIncomeMember |
| Other [Member] | Miscellaneous income [Member]                                                      |                                                                                                                                                                                                                                                                                       |   |
| **Derivative Instruments, Gain (Loss) [Line Items]**                                                |                                                                                                                                                                                                                                                                                       |   |
| Gain (loss) recognized on all derivatives                                                           | $ (1,445)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_OtherContractMember/ us-gaap_IncomeStatementLocationAxis= sov_MiscellaneousIncomeMember                                                                                                  | $ (648)us-gaap_DerivativeGainLossOnDerivativeNet/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_OtherContractMember/ us-gaap_IncomeStatementLocationAxis= sov_MiscellaneousIncomeMember |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5618551-113959Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (a),(c),(d),(e) -URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624171-113959
+ Details**Name:**us-gaap_DerivativeGainLossOnDerivativeNet**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeInstrumentsGainLossLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeInstrumentRiskAxis=sov_CustomerRelatedDerivativesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeInstrumentRiskAxis=sov_ForwardCommitmentsToSellLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeInstrumentRiskAxis=sov_MortgageServicingRightsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeInstrumentRiskAxis=sov_SCUSADerivativesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CurrencySwapMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeContractMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateLockCommitmentsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_DerivativeInstrumentRiskAxis=us-gaap_OtherContractMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |