| **COMMITMENTS, CONTINGENCIES, AND GUARANTEES (SC Commitments) (Details) - USD ($)**                                                         |             | 6 Months Ended |               |               |              |
|---------------------------------------------------------------------------------------------------------------------------------------------|-------------|----------------|---------------|---------------|--------------|
||
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Guarantees, fair value                                                                                                                      |        | $ 5,100,000    |          |          |         |
| Minimum sales commitment, charged off loan receivables                                                                                      |        | 275,000,000    |          | $ 200,000,000 |         |
| Minimum sales commitment, loans receivable, written off, remaining                                                                          |        | 216,400,000    |          |          |         |
| Civil fine [Member] | Violation of service members civil relief act [Member]                                                                |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Civil fine, amount                                                                                                                          | $ 55,000    |           |          |          |         |
| Lost equity for each repossession [Member] | Violation of service members civil relief act [Member]                                         |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Civil fine, amount                                                                                                                          | 10,000      |           |          |          |         |
| Sought to collect repossession-related fees [Member] | Violation of service members civil relief act [Member]                               |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Civil fine, amount                                                                                                                          | 5,000       |           |          |          |         |
| Minimum [Member] | Civil fine to affected service members [Member] | Violation of service members civil relief act [Member]                 |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Civil fine, amount                                                                                                                          | $ 9,400,000 |           |          |          |         |
| Forward commitments to sell loans [Member]                                                                                                  |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Total commitments                                                                                                                           |        | $ 108,686,000  |          |          | $ 82,791,000 |
| SCUSA [Member] | Maximum [Member] | Citizens Bank of Pennsylvania [Member]                                                                  |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Loss-sharing payment percentage                                                                                                             |        | 0.50%          |          |          |         |
| SCUSA [Member] | Loan purchase commitments [Member]                                                                                         |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Loan purchase commitment, cancellation period                                                                                               |        | 90 days        |          |          |         |
| SCUSA [Member] | Loan purchase commitments [Member] | Minimum [Member] | Citizens Bank of Pennsylvania [Member]                             |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Loan purchase commitment amount                                                                                                             |        | $ 250,000,000  |          |          |         |
| SCUSA [Member] | Loan purchase commitments [Member] | Minimum [Member] | Citizens Bank of Pennsylvania [Member] | Subsequent Event [Member] |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Loan purchase commitment amount                                                                                                             |        |           | $ 50,000,000  |          |         |
| SCUSA [Member] | Loan purchase commitments [Member] | Maximum [Member] | Citizens Bank of Pennsylvania [Member]                             |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Loan purchase commitment amount                                                                                                             |        | 600,000,000    |          |          |         |
| SCUSA [Member] | Loan purchase commitments [Member] | Maximum [Member] | Citizens Bank of Pennsylvania [Member] | Subsequent Event [Member] |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Loan purchase commitment amount                                                                                                             |        |           | $ 200,000,000 |          |         |
| SCUSA [Member] | Loan purchase commitments [Member] | July 2014 to July 2015 [Member] | Minimum [Member]                                    |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Loan purchase commitment amount                                                                                                             |        | $ 30,000,000   |          |          |         |
| Loan purchase commitment, as a percentage of lending entity's near-prime originations                                                       |        | 75.00%         |          |          |         |
| SCUSA [Member] | Loan purchase commitments [Member] | July 2014 to July 2017 [Member] | Minimum [Member]                                    |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Loan purchase commitment amount                                                                                                             |        | $ 30,000,000   |          |          |         |
| Loan purchase commitment, as a percentage of lending entity's near-prime originations                                                       |        | 50.00%         |          |          |         |
| SCUSA [Member] | Forward commitments to sell loans [Member] | Obligation to repurchase receivables sold [Member]                            |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Total commitments                                                                                                                           |        | $ 7,900,000    |          |          | $ 7,700,000  |
| SCUSA [Member] | Forward commitments to sell loans [Member] | Maximum [Member]                                                              |        |           |          |          |         |
| **Long-term Purchase Commitment [Line Items]**                                                                                              |        |           |          |          |         |
| Total commitments                                                                                                                           |        | $ 300,000,000  |          |          |         |

| X                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Represents amount committed under commitments.
+ References
No definition available.
+ Details**Name:**sov_CommitmentsAmountCommitted**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loan Purchase Commitment, Amount
+ References
No definition available.
+ Details**Name:**sov_LoanPurchaseCommitmentAmount**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loan Purchase Commitment, Cancellation Period
+ References
No definition available.
+ Details**Name:**sov_LoanPurchaseCommitmentCancellationPeriod**Namespace Prefix:**sov_**Data Type:**xbrli:durationItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loan Purchase Commitment, Percentage of Lending Entity's Near-Prime Originations
+ References
No definition available.
+ Details**Name:**sov_LoanPurchaseCommitmentPercentageofLendingEntitysNearPrimeOriginations**Namespace Prefix:**sov_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Minimum Sales Commitment, Loans Receivable, Written Off
+ References
No definition available.
+ Details**Name:**sov_MinimumSalesCommitmentLoansReceivableWrittenOff**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Minimum Sales Commitment, Loans Receivable, Written Off, Remaining
+ References
No definition available.
+ Details**Name:**sov_MinimumSalesCommitmentLoansReceivableWrittenOffRemaining**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Profit (Loss) Sharing Payment, Percentage
+ References
No definition available.
+ Details**Name:**sov_ProfitLossSharingPaymentPercentage**Namespace Prefix:**sov_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value portion of guarantee, including, but not limited to, financial standby letter of credit, fair value guarantee, guarantee of collection of scheduled contractual cash flows from financial assets, and contracts that contingently require the guarantor to make payments or perform services.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12201-110248
+ Details**Name:**us-gaap_GuaranteesFairValueDisclosure**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**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_LongTermPurchaseCommitmentLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The value (monetary amount) of the award the plaintiff seeks in the legal matter.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349
+ Details**Name:**us-gaap_LossContingencyDamagesSoughtValue**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LossContingenciesByNatureOfContingencyAxis=sov_CivilFineMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LitigationCaseAxis=sov_ViolationofServiceMembersCivilReliefActMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LossContingenciesByNatureOfContingencyAxis=sov_LostEquityforEachRepossessionMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                           |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LossContingenciesByNatureOfContingencyAxis=sov_SoughttoCollectRepossessionrelatedFeesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_RangeAxis=us-gaap_MinimumMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LossContingenciesByNatureOfContingencyAxis=sov_CivilFinetoAffectedServiceMembersMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**sov_CommitmentsTypeAxis=sov_ForwardCommitmentsToSellLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=sov_SCMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_RangeAxis=us-gaap_MaximumMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**dei_LegalEntityAxis=sov_CitizensBankofPennsylvaniaMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**sov_CommitmentsTypeAxis=us-gaap_LoanPurchaseCommitmentsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**sov_EffectivePeriodsAxis=sov_July2014toJuly2015Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**sov_EffectivePeriodsAxis=sov_July2014toJuly2017Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_ObligationToRepurchaseReceivablesSoldMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |