| **FAIR VALUE (Fair Value Option Disclosure) (Details) (USD $)In Thousands, unless otherwise specified** | 3 Months Ended                                                                                                                                                                                       | 0 Months Ended                                                                                                                                                                            |                                                                                                                                                                                                                |
|---------------------------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**        |                                                                                                                                                                                                 |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Mortgage servicing rights                                                                               | $ 135,452us-gaap_ServicingAssetAtFairValueAmount                                                                                                                                                     |                                                                                                                                                                                      |                                                                                                                                                                                                           | $ 145,047us-gaap_ServicingAssetAtFairValueAmount |
| Residential mortgages [Member]                                                                          |                                                                                                                                                                                                 |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**        |                                                                                                                                                                                                 |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Mortgage servicing rights                                                                               | 135,500us-gaap_ServicingAssetAtFairValueAmount/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember                                                                                   |                                                                                                                                                                                      |                                                                                                                                                                                                           | 145,000us-gaap_ServicingAssetAtFairValueAmount/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember |
| Change in fair value due to valuation assumptions                                                       | (6,990)us-gaap_ServicingAssetAtFairValueChangesInFairValueResultingFromChangesInValuationInputsOrChangesInAssumptions/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember            | (4,459)us-gaap_ServicingAssetAtFairValueChangesInFairValueResultingFromChangesInValuationInputsOrChangesInAssumptions/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember |                                                                                                                                                                                                           |   |
| Residential mortgages [Member] | Mortgage servicing rights [Member]                                     |                                                                                                                                                                                                 |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**        |                                                                                                                                                                                                 |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Mortgage servicing rights                                                                               | 135,500us-gaap_ServicingAssetAtFairValueAmount/ us-gaap_EligibleItemOrGroupForFairValueOptionAxis= sov_ServicingAssetsMember/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember     |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Residential mortgage loans held for sale [Member]                                                       |                                                                                                                                                                                                 |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**        |                                                                                                                                                                                                 |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Fair Value, Loans held for sale                                                                         | 316,026sov_FairValueOptionLoansHeldforSaleAggregateAmount/ us-gaap_FairValueByAssetClassAxis= sov_LoansHeldForSaleMember                                                                             |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Aggregate Unpaid Principal Balance, Loans held for sale                                                 | 311,533sov_LoansHeldForSaleUnpaidPrincipalBalance/ us-gaap_FairValueByAssetClassAxis= sov_LoansHeldForSaleMember                                                                                     |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Difference, Loans held for sale                                                                         | 4,493sov_FairValueOptionLoansHeldforSaleAggregatedDifference/ us-gaap_FairValueByAssetClassAxis= sov_LoansHeldForSaleMember                                                                          |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Fair Value, Nonaccrual loans                                                                            | 0sov_FairValueOptionLoansHeldforSaleAggregateAmountinNonaccrualStatus/ us-gaap_FairValueByAssetClassAxis= sov_LoansHeldForSaleMember                                                                 |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Aggregate Unpaid Principal Balance, Nonaccrual loans                                                    | 0sov_FairValueOptionLoansHeldforSaleAggregateAmountinNonaccrualStatusAggregateUnpaidPrincipalBalance/ us-gaap_FairValueByAssetClassAxis= sov_LoansHeldForSaleMember                                  |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Difference, Nonaccrual loans                                                                            | 0sov_FairValueOptionLoansHeldforSaleAggregateAmountinNonaccrualStatusAggregatedDifference/ us-gaap_FairValueByAssetClassAxis= sov_LoansHeldForSaleMember                                             |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Threshold period for discontinuing and reversing accrual of interest (more than)                        | 90 days                                                                                                                                                                                              |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Retail installment contracts held for investment [Member]                                               |                                                                                                                                                                                                 |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**        |                                                                                                                                                                                                 |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Fair Value, Retail installment contracts held for investment                                            | 676,097sov_FairValueOptionLoansHeldasAssetsAggregateAmount/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember                                                 |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Aggregate Unpaid Principal Balance, Retail installment contracts held for investment                    | 873,481sov_FairValueOptionLoansHeldasAssetsAggregateUnpaidPrincipalBalance/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember                                 |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Difference, Retail installment contracts held for investment                                            | (197,384)sov_FairValueOptionLoansHeldasAssetsAggregatedDifference/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember                                          |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Fair Value, Nonaccrual loans                                                                            | 51,474us-gaap_FairValueOptionLoansHeldAsAssetsAggregateAmountInNonaccrualStatus/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember                            |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Aggregate Unpaid Principal Balance, Nonaccrual loans                                                    | 88,859sov_FairValueOptionLoansHeldasAssetsAggregateAmountinNonaccrualStatusAggregateUnpaidPrincipalBalance/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Difference, Nonaccrual loans                                                                            | (37,385)us-gaap_FairValueOptionLoansHeldAsAssetsAggregateAmountInNonaccrualStatusAggregatedDifference/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember      |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Threshold period for discontinuing and reversing accrual of interest (more than)                        | 60 days                                                                                                                                                                                              |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| SCUSA [Member] | Retail installment contracts held for investment [Member]                              |                                                                                                                                                                                                 |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]**        |                                                                                                                                                                                                 |                                                                                                                                                                                      |                                                                                                                                                                                                           |   |
| Fair Value, Retail installment contracts held for investment                                            |                                                                                                                                                                                                 |                                                                                                                                                                                      | 1,900,000sov_FairValueOptionLoansHeldasAssetsAggregateAmount/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember/ dei_LegalEntityAxis= sov_ScusaMember                   |   |
| Aggregate Unpaid Principal Balance, Retail installment contracts held for investment                    |                                                                                                                                                                                                 |                                                                                                                                                                                      | $ 2,600,000sov_FairValueOptionLoansHeldasAssetsAggregateUnpaidPrincipalBalance/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember/ dei_LegalEntityAxis= sov_ScusaMember |   |
| Threshold period for discontinuing and reversing accrual of interest (more than)                        |                                                                                                                                                                                                 |                                                                                                                                                                                      | 60 days                                                                                                                                                                                                        |   |

| X                                                                                                                                                                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair Value, Option, Loans Held as Assets, Aggregate Amount
+ References
No definition available.
+ Details**Name:**sov_FairValueOptionLoansHeldasAssetsAggregateAmount**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair Value, Option, Loans Held as Assets, Aggregate Amount in Nonaccrual Status, Aggregate Unpaid Principal Balance
+ References
No definition available.
+ Details**Name:**sov_FairValueOptionLoansHeldasAssetsAggregateAmountinNonaccrualStatusAggregateUnpaidPrincipalBalance**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair Value, Option, Loans Held as Assets, Aggregated Difference
+ References
No definition available.
+ Details**Name:**sov_FairValueOptionLoansHeldasAssetsAggregatedDifference**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair Value, Option, Loans Held as Assets, Aggregate Unpaid Principal Balance
+ References
No definition available.
+ Details**Name:**sov_FairValueOptionLoansHeldasAssetsAggregateUnpaidPrincipalBalance**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair Value, Option, Loans Held for Sale, Aggregate Amount
+ References
No definition available.
+ Details**Name:**sov_FairValueOptionLoansHeldforSaleAggregateAmount**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair Value, Option, Loans Held for Sale, Aggregate Amount in Nonaccrual Status
+ References
No definition available.
+ Details**Name:**sov_FairValueOptionLoansHeldforSaleAggregateAmountinNonaccrualStatus**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                             |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair Value, Option, Loans Held for Sale, Aggregate Amount in Nonaccrual Status, Aggregated Difference
+ References
No definition available.
+ Details**Name:**sov_FairValueOptionLoansHeldforSaleAggregateAmountinNonaccrualStatusAggregatedDifference**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair Value, Option, Loans Held for Sale, Aggregate Amount in Nonaccrual Status, Aggregate Unpaid Principal Balance
+ References
No definition available.
+ Details**Name:**sov_FairValueOptionLoansHeldforSaleAggregateAmountinNonaccrualStatusAggregateUnpaidPrincipalBalance**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair Value, Option, Loans Held for Sale, Aggregated Difference
+ References
No definition available.
+ Details**Name:**sov_FairValueOptionLoansHeldforSaleAggregatedDifference**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Unpaid principal balance of loans held-for-sale.
+ References
No definition available.
+ Details**Name:**sov_LoansHeldForSaleUnpaidPrincipalBalance**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Threshold Period for Discontinuing and Reversing Interest Accrual
+ References
No definition available.
+ Details**Name:**sov_ThresholdPeriodforDiscontinuingandReversingInterestAccrual**Namespace Prefix:**sov_**Data Type:**xbrli:durationItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This item represents the aggregate fair value of loans held as assets that are in nonaccrual status for which the fair value option has been elected, if the entity's policy is to recognize interest income separately from other changes in fair value.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 28 -Subparagraph (e)(2) -URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14064-108612
+ Details**Name:**us-gaap_FairValueOptionLoansHeldAsAssetsAggregateAmountInNonaccrualStatus**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
For loans held as assets for which the fair value option has been elected, this item represents the difference between the aggregate fair value and the aggregate unpaid principal balance of those loans that are in nonaccrual status.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 28 -Subparagraph (e)(3) -URI http://asc.fasb.org/extlink&oid=6957238&loc=d3e14064-108612
+ Details**Name:**us-gaap_FairValueOptionLoansHeldAsAssetsAggregateAmountInNonaccrualStatusAggregatedDifference**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746
+ Details**Name:**us-gaap_ServicingAssetAtFairValueAmount**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The net Increase or Decrease in fair value as a result of changes in the inputs, assumptions, or model used to calculate the fair value of servicing assets.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 3 -Subparagraph (a)(4)(i) -URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746
+ Details**Name:**us-gaap_ServicingAssetAtFairValueChangesInFairValueResultingFromChangesInValuationInputsOrChangesInAssumptions**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**dei_LegalEntityAxis=sov_ScusaMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueByAssetClassAxis=sov_LoansHeldForSaleMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueByAssetClassAxis=sov_RetailInstallmentContractsHeldforinvestmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |