| **VARIABLE INTEREST ENTITIES (Cash Flow Summary) (Details) (USD $)In Thousands, unless otherwise specified** | 2 Months Ended                                                                                                                                                                                                                                              | 3 Months Ended                                                                                                                                                                                                                                        |
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| Trusts [Member]                                                                                              |                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                  |
| **Variable Interest Entity [Line Items]**                                                                    |                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                  |
| Receivables securitized                                                                                      | $ 1,574,084us-gaap_ProceedsFromAccountsReceivableSecuritization/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_TrustsMember                                        | $ 3,981,855us-gaap_ProceedsFromAccountsReceivableSecuritization/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_TrustsMember                                  |
| Net proceeds from new securitizations                                                                        | 1,238,202us-gaap_CashFlowsBetweenTransfereeAndTransferorProceedsFromNewTransfers/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_TrustsMember                       | 3,060,862us-gaap_CashFlowsBetweenTransfereeAndTransferorProceedsFromNewTransfers/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_TrustsMember                 |
| Cash received for servicing fees                                                                             | 97,932us-gaap_CashFlowsBetweenTransfereeAndTransferorServicingFees/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_TrustsMember                                     | 159,802us-gaap_CashFlowsBetweenTransfereeAndTransferorServicingFees/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_TrustsMember                              |
| Cash received upon release from reserved and restricted cash accounts                                        | 165sov_ProceedsReceivedfromReservedandRestrictedCash/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_TrustsMember                                                   | 0sov_ProceedsReceivedfromReservedandRestrictedCash/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_TrustsMember                                               |
| Net distributions from Trusts                                                                                | 241,251sov_DistributionsReceivedfromVariableInterestEntity/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_TrustsMember                                             | 300,487sov_DistributionsReceivedfromVariableInterestEntity/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_TrustsMember                                       |
| Total cash received from securitization trusts                                                               | 1,577,550sov_CashFlowsBetweenTransferorandTransferee/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_TrustsMember                                                   | 3,521,151sov_CashFlowsBetweenTransferorandTransferee/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_TrustsMember                                             |
| Off-balance Securitization Trusts [Member]                                                                   |                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                  |
| **Variable Interest Entity [Line Items]**                                                                    |                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                  |
| Receivables securitized                                                                                      | 774,183us-gaap_ProceedsFromAccountsReceivableSecuritization/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_OffbalanceSecuritizationTrustsMember                    | 0us-gaap_ProceedsFromAccountsReceivableSecuritization/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_OffbalanceSecuritizationTrustsMember                    |
| Net proceeds from new securitizations                                                                        | 815,850us-gaap_CashFlowsBetweenTransfereeAndTransferorProceedsFromNewTransfers/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_OffbalanceSecuritizationTrustsMember | 0us-gaap_CashFlowsBetweenTransfereeAndTransferorProceedsFromNewTransfers/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_OffbalanceSecuritizationTrustsMember |
| Cash received for servicing fees                                                                             | 2,788us-gaap_CashFlowsBetweenTransfereeAndTransferorServicingFees/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_OffbalanceSecuritizationTrustsMember              | 5,304us-gaap_CashFlowsBetweenTransfereeAndTransferorServicingFees/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_OffbalanceSecuritizationTrustsMember        |
| Total cash received from securitization trusts                                                               | $ 818,638sov_CashFlowsBetweenTransferorandTransferee/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_OffbalanceSecuritizationTrustsMember                           | $ 5,304sov_CashFlowsBetweenTransferorandTransferee/ us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis= sov_OffbalanceSecuritizationTrustsMember                       |

| X                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Cash Flows Between Transferor and Transferee
+ References
No definition available.
+ Details**Name:**sov_CashFlowsBetweenTransferorandTransferee**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                        |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Distributions Received from Variable Interest Entity
+ References
No definition available.
+ Details**Name:**sov_DistributionsReceivedfromVariableInterestEntity**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Proceeds Received from Reserved and Restricted Cash
+ References
No definition available.
+ Details**Name:**sov_ProceedsReceivedfromReservedandRestrictedCash**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Cash Flows between a transferor and a transferee attributable to newly transferred assets related to either a securitization, asset-backed financing arrangement, or similar transfer in which the transferor has continuing involvement with the transferred financial assets underlying the transaction (including, but not limited to, servicing, recourse, and restrictions on transferor's interests in the transferred financial assets).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph b -URI http://asc.fasb.org/extlink&oid=13989330&loc=d3e107207-111719
+ Details**Name:**us-gaap_CashFlowsBetweenTransfereeAndTransferorProceedsFromNewTransfers**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Cash Flows between a transferee and a transferor attributable to servicing fees related to a securitization, asset-backed financing arrangement, or similar transfer in which the transferor has continuing involvement with the transferred financial assets underlying the transaction (including, but not limited to, servicing, recourse, and restrictions on transferor's interests in the transferred financial assets).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph d -URI http://asc.fasb.org/extlink&oid=13989330&loc=d3e107207-111719
+ Details**Name:**us-gaap_CashFlowsBetweenTransfereeAndTransferorServicingFees**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Proceeds from securitizations of receivables treated as collateralized borrowings, which are classified as financing transactions.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585
+ Details**Name:**us-gaap_ProceedsFromAccountsReceivableSecuritization**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_VariableInterestEntityLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis=sov_OffbalanceSecuritizationTrustsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_QualitativeAndQuantitativeInformationTransferorsContinuingInvolvementTransferredFinancialAssetsByTransferOrTransfereeAxis=sov_TrustsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |