| **BUSINESS SEGMENT INFORMATION (Segment Reporting Information) (Details) (USD $)** | 3 Months Ended                                                                                                                                                                                                                                                                 | 0 Months Ended                                                                                                                                                                                                                                                                  |
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| **Segment Reporting Information [Line Items]**                                     |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| Net interest income                                                                | $ 1,654,159,000us-gaap_InterestIncomeExpenseNet                                                                                                                                                                                                                                | $ 1,172,105,000us-gaap_InterestIncomeExpenseNet                                                                                                                                                                                                                                 |   |
| Total non-interest income                                                          | 665,397,000us-gaap_NoninterestIncome                                                                                                                                                                                                                                           | 2,861,256,000us-gaap_NoninterestIncome                                                                                                                                                                                                                                          |   |
| Total non-interest income                                                          |                                                                                                                                                                                                                                                                           | 432,717,000sov_FeesandOtherIncomeIncludingRealizedGainsLossesonSaleofInvestmentSecurities                                                                                                                                                                                       |   |
| Gain on change in control                                                          | 0sov_GainonChangeinControl                                                                                                                                                                                                                                                     | 2,428,539,000sov_GainonChangeinControl                                                                                                                                                                                                                                          |   |
| Provision for credit losses                                                        | 872,184,000us-gaap_ProvisionForLoanLeaseAndOtherLosses                                                                                                                                                                                                                         | 335,330,000us-gaap_ProvisionForLoanLeaseAndOtherLosses                                                                                                                                                                                                                          |   |
| Total expenses                                                                     | 1,082,360,000sov_GeneralAndAdministrativeAndOtherExpenses                                                                                                                                                                                                                      | 770,281,000sov_GeneralAndAdministrativeAndOtherExpenses                                                                                                                                                                                                                         |   |
| Income/(loss) before income taxes                                                  | 365,012,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest                                                                                                                                                                 | 2,927,750,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest                                                                                                                                                                |   |
| Intersegment (expense)/revenue                                                     | 0us-gaap_Revenues                                                                                                                                                                                                                                                              | 0us-gaap_Revenues                                                                                                                                                                                                                                                               |   |
| Total average assets                                                               | 118,822,451,000sov_SegmentReportingInformationAverageAssets1                                                                                                                                                                                                                   | 96,780,130,000sov_SegmentReportingInformationAverageAssets1                                                                                                                                                                                                                     |   |
| Chrysler Group [Member]                                                            |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| **Segment Reporting Information [Line Items]**                                     |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| Private label financing agreement, term                                            |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            | 10 years |
| Eliminations [Member]                                                              |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| **Segment Reporting Information [Line Items]**                                     |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| Net interest income                                                                | 87,000us-gaap_InterestIncomeExpenseNet/ us-gaap_ConsolidationItemsAxis= us-gaap_ConsolidationEliminationsMember                                                                                                                                                                | (344,136,000)us-gaap_InterestIncomeExpenseNet/ us-gaap_ConsolidationItemsAxis= us-gaap_ConsolidationEliminationsMember                                                                                                                                                          |   |
| Total non-interest income                                                          | (10,093,000)us-gaap_NoninterestIncome/ us-gaap_ConsolidationItemsAxis= us-gaap_ConsolidationEliminationsMember                                                                                                                                                                 | (60,004,000)us-gaap_NoninterestIncome/ us-gaap_ConsolidationItemsAxis= us-gaap_ConsolidationEliminationsMember                                                                                                                                                                  |   |
| Provision for credit losses                                                        | 0us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_ConsolidationItemsAxis= us-gaap_ConsolidationEliminationsMember                                                                                                                                                          | (225,454,000)us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_ConsolidationItemsAxis= us-gaap_ConsolidationEliminationsMember                                                                                                                                               |   |
| Total expenses                                                                     | (8,046,000)sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_ConsolidationItemsAxis= us-gaap_ConsolidationEliminationsMember                                                                                                                                               | (245,611,000)sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_ConsolidationItemsAxis= us-gaap_ConsolidationEliminationsMember                                                                                                                                              |   |
| Income/(loss) before income taxes                                                  | (1,960,000)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_ConsolidationItemsAxis= us-gaap_ConsolidationEliminationsMember                                                                                        | 66,925,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_ConsolidationItemsAxis= us-gaap_ConsolidationEliminationsMember                                                                                          |   |
| Intersegment (expense)/revenue                                                     | 0us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_ConsolidationEliminationsMember                                                                                                                                                                                     | 0us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_ConsolidationEliminationsMember                                                                                                                                                                                      |   |
| Total average assets                                                               | 0sov_SegmentReportingInformationAverageAssets1/ us-gaap_ConsolidationItemsAxis= us-gaap_ConsolidationEliminationsMember                                                                                                                                                        | 0sov_SegmentReportingInformationAverageAssets1/ us-gaap_ConsolidationItemsAxis= us-gaap_ConsolidationEliminationsMember                                                                                                                                                         |   |
| SCUSA [Member]                                                                     |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| **Segment Reporting Information [Line Items]**                                     |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| Net interest income                                                                | 1,160,005,000us-gaap_InterestIncomeExpenseNet/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                                                                                           | 1,062,202,000us-gaap_InterestIncomeExpenseNet/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                                                                                            |   |
| Total non-interest income                                                          | 422,970,000us-gaap_NoninterestIncome/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                                                                                                    | 239,311,000us-gaap_NoninterestIncome/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                                                                                                     |   |
| Provision for credit losses                                                        | 605,982,000us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                                                                                  | 698,578,000us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                                                                                   |   |
| Total expenses                                                                     | 546,318,000sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                                                                                 | 473,583,000sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                                                                                  |   |
| Income/(loss) before income taxes                                                  | 430,675,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                          | 129,352,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                           |   |
| Intersegment (expense)/revenue                                                     | 0us-gaap_Revenues/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                                                                                                                       | 0us-gaap_Revenues/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                                                                                                                        |   |
| Total average assets                                                               | 32,940,082,000sov_SegmentReportingInformationAverageAssets1/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                                                                             | 18,287,600,000sov_SegmentReportingInformationAverageAssets1/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                                                                              |   |
| SCUSA [Member] | Purchase Price Adjustments [Member]                               |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| **Segment Reporting Information [Line Items]**                                     |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| Net interest income                                                                | 94,768,000us-gaap_InterestIncomeExpenseNet/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                      | 70,991,000us-gaap_InterestIncomeExpenseNet/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                       |   |
| Total non-interest income                                                          | 38,317,000us-gaap_NoninterestIncome/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                             |                                                                                                                                                                                                                                                                            |   |
| Total non-interest income                                                          |                                                                                                                                                                                                                                                                           | 83,228,000sov_FeesandOtherIncomeIncludingRealizedGainsLossesonSaleofInvestmentSecurities/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                         |   |
| Gain on change in control                                                          |                                                                                                                                                                                                                                                                           | 2,428,539,000sov_GainonChangeinControl/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                           |   |
| Provision for credit losses                                                        | 219,202,000us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                          | (137,794,000)us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                         |   |
| Total expenses                                                                     | (7,142,000)sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                         | 90,549,000sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                           |   |
| Income/(loss) before income taxes                                                  | (78,975,000)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember | 2,630,003,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember |   |
| Intersegment (expense)/revenue                                                     | 0us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                                               | 0us-gaap_Revenues/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                                                |   |
| Total average assets                                                               | 0sov_SegmentReportingInformationAverageAssets1/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                  | 0sov_SegmentReportingInformationAverageAssets1/ us-gaap_ConsolidationItemsAxis= us-gaap_MaterialReconcilingItemsMember/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis= sov_ScusaMember                                                                   |   |
| Retail Banking [Member]                                                            |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| **Segment Reporting Information [Line Items]**                                     |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| Net interest income                                                                | 190,460,000us-gaap_InterestIncomeExpenseNet/ us-gaap_StatementBusinessSegmentsAxis= sov_RetailBankingMember                                                                                                                                                                    | 213,065,000us-gaap_InterestIncomeExpenseNet/ us-gaap_StatementBusinessSegmentsAxis= sov_RetailBankingMember                                                                                                                                                                     |   |
| Total non-interest income                                                          | 69,981,000us-gaap_NoninterestIncome/ us-gaap_StatementBusinessSegmentsAxis= sov_RetailBankingMember                                                                                                                                                                            | 86,893,000us-gaap_NoninterestIncome/ us-gaap_StatementBusinessSegmentsAxis= sov_RetailBankingMember                                                                                                                                                                             |   |
| Provision for credit losses                                                        | 19,595,000us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_StatementBusinessSegmentsAxis= sov_RetailBankingMember                                                                                                                                                          | 9,209,000us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_StatementBusinessSegmentsAxis= sov_RetailBankingMember                                                                                                                                                            |   |
| Total expenses                                                                     | 284,968,000sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_StatementBusinessSegmentsAxis= sov_RetailBankingMember                                                                                                                                                        | 254,535,000sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_StatementBusinessSegmentsAxis= sov_RetailBankingMember                                                                                                                                                         |   |
| Income/(loss) before income taxes                                                  | (44,122,000)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_StatementBusinessSegmentsAxis= sov_RetailBankingMember                                                                                                | 36,214,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_StatementBusinessSegmentsAxis= sov_RetailBankingMember                                                                                                   |   |
| Intersegment (expense)/revenue                                                     | 67,154,000us-gaap_Revenues/ us-gaap_StatementBusinessSegmentsAxis= sov_RetailBankingMember                                                                                                                                                                                     | 62,611,000us-gaap_Revenues/ us-gaap_StatementBusinessSegmentsAxis= sov_RetailBankingMember                                                                                                                                                                                      |   |
| Total average assets                                                               | 18,099,568,000sov_SegmentReportingInformationAverageAssets1/ us-gaap_StatementBusinessSegmentsAxis= sov_RetailBankingMember                                                                                                                                                    | 18,796,940,000sov_SegmentReportingInformationAverageAssets1/ us-gaap_StatementBusinessSegmentsAxis= sov_RetailBankingMember                                                                                                                                                     |   |
| Auto Finance & Alliances [Member]                                              |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| **Segment Reporting Information [Line Items]**                                     |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| Net interest income                                                                | 19,263,000us-gaap_InterestIncomeExpenseNet/ us-gaap_StatementBusinessSegmentsAxis= sov_AutoFinanceandAlliancesMember                                                                                                                                                           | 18,865,000us-gaap_InterestIncomeExpenseNet/ us-gaap_StatementBusinessSegmentsAxis= sov_AutoFinanceandAlliancesMember                                                                                                                                                            |   |
| Total non-interest income                                                          | 82,172,000us-gaap_NoninterestIncome/ us-gaap_StatementBusinessSegmentsAxis= sov_AutoFinanceandAlliancesMember                                                                                                                                                                  | 6,060,000us-gaap_NoninterestIncome/ us-gaap_StatementBusinessSegmentsAxis= sov_AutoFinanceandAlliancesMember                                                                                                                                                                    |   |
| Provision for credit losses                                                        | 2,931,000us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_StatementBusinessSegmentsAxis= sov_AutoFinanceandAlliancesMember                                                                                                                                                 | (5,000)us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_StatementBusinessSegmentsAxis= sov_AutoFinanceandAlliancesMember                                                                                                                                                    |   |
| Total expenses                                                                     | 78,127,000sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_StatementBusinessSegmentsAxis= sov_AutoFinanceandAlliancesMember                                                                                                                                               | 10,436,000sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_StatementBusinessSegmentsAxis= sov_AutoFinanceandAlliancesMember                                                                                                                                                |   |
| Income/(loss) before income taxes                                                  | 20,377,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_StatementBusinessSegmentsAxis= sov_AutoFinanceandAlliancesMember                                                                                        | 14,494,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_StatementBusinessSegmentsAxis= sov_AutoFinanceandAlliancesMember                                                                                         |   |
| Intersegment (expense)/revenue                                                     | (6,640,000)us-gaap_Revenues/ us-gaap_StatementBusinessSegmentsAxis= sov_AutoFinanceandAlliancesMember                                                                                                                                                                          | (2,152,000)us-gaap_Revenues/ us-gaap_StatementBusinessSegmentsAxis= sov_AutoFinanceandAlliancesMember                                                                                                                                                                           |   |
| Total average assets                                                               | 5,037,233,000sov_SegmentReportingInformationAverageAssets1/ us-gaap_StatementBusinessSegmentsAxis= sov_AutoFinanceandAlliancesMember                                                                                                                                           | 2,348,331,000sov_SegmentReportingInformationAverageAssets1/ us-gaap_StatementBusinessSegmentsAxis= sov_AutoFinanceandAlliancesMember                                                                                                                                            |   |
| Real Estate and Commercial Banking [Member]                                        |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| **Segment Reporting Information [Line Items]**                                     |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| Net interest income                                                                | 126,720,000us-gaap_InterestIncomeExpenseNet/ us-gaap_StatementBusinessSegmentsAxis= sov_RealEstateandCommercialBankingMember                                                                                                                                                   | 118,689,000us-gaap_InterestIncomeExpenseNet/ us-gaap_StatementBusinessSegmentsAxis= sov_RealEstateandCommercialBankingMember                                                                                                                                                    |   |
| Total non-interest income                                                          | 22,080,000us-gaap_NoninterestIncome/ us-gaap_StatementBusinessSegmentsAxis= sov_RealEstateandCommercialBankingMember                                                                                                                                                           | 26,342,000us-gaap_NoninterestIncome/ us-gaap_StatementBusinessSegmentsAxis= sov_RealEstateandCommercialBankingMember                                                                                                                                                            |   |
| Provision for credit losses                                                        | (9,766,000)us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_StatementBusinessSegmentsAxis= sov_RealEstateandCommercialBankingMember                                                                                                                                        | 4,667,000us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_StatementBusinessSegmentsAxis= sov_RealEstateandCommercialBankingMember                                                                                                                                           |   |
| Total expenses                                                                     | 53,928,000sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_StatementBusinessSegmentsAxis= sov_RealEstateandCommercialBankingMember                                                                                                                                        | 46,432,000sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_StatementBusinessSegmentsAxis= sov_RealEstateandCommercialBankingMember                                                                                                                                         |   |
| Income/(loss) before income taxes                                                  | 104,638,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_StatementBusinessSegmentsAxis= sov_RealEstateandCommercialBankingMember                                                                                | 93,932,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_StatementBusinessSegmentsAxis= sov_RealEstateandCommercialBankingMember                                                                                  |   |
| Intersegment (expense)/revenue                                                     | (72,433,000)us-gaap_Revenues/ us-gaap_StatementBusinessSegmentsAxis= sov_RealEstateandCommercialBankingMember                                                                                                                                                                  | (83,738,000)us-gaap_Revenues/ us-gaap_StatementBusinessSegmentsAxis= sov_RealEstateandCommercialBankingMember                                                                                                                                                                   |   |
| Total average assets                                                               | 22,969,672,000sov_SegmentReportingInformationAverageAssets1/ us-gaap_StatementBusinessSegmentsAxis= sov_RealEstateandCommercialBankingMember                                                                                                                                   | 22,374,949,000sov_SegmentReportingInformationAverageAssets1/ us-gaap_StatementBusinessSegmentsAxis= sov_RealEstateandCommercialBankingMember                                                                                                                                    |   |
| Global Banking & Markets and Large Corporate [Member]                          |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| **Segment Reporting Information [Line Items]**                                     |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| Minimum annual revenue to service corporations                                     | 500,000,000sov_MinimumAnnualRevenuetoServiceCorporation/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                                                                       |                                                                                                                                                                                                                                                                            |   |
| Net interest income                                                                | 49,164,000us-gaap_InterestIncomeExpenseNet/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                                                                                    | 41,591,000us-gaap_InterestIncomeExpenseNet/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                                                                                     |   |
| Total non-interest income                                                          | 17,584,000us-gaap_NoninterestIncome/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                                                                                           | 22,524,000us-gaap_NoninterestIncome/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                                                                                            |   |
| Provision for credit losses                                                        | 3,221,000us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                                                                          | 2,438,000us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                                                                           |   |
| Total expenses                                                                     | 23,073,000sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                                                                        | 17,130,000sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                                                                         |   |
| Income/(loss) before income taxes                                                  | 40,454,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                 | 44,547,000us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                  |   |
| Intersegment (expense)/revenue                                                     | (9,251,000)us-gaap_Revenues/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                                                                                                   | (9,040,000)us-gaap_Revenues/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                                                                                                    |   |
| Total average assets                                                               | 10,595,017,000sov_SegmentReportingInformationAverageAssets1/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                                                                   | 8,443,066,000sov_SegmentReportingInformationAverageAssets1/ us-gaap_StatementBusinessSegmentsAxis= sov_GlobalBankingandLargeCorporateMember                                                                                                                                     |   |
| Other [Member]                                                                     |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| **Segment Reporting Information [Line Items]**                                     |                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                            |   |
| Net interest income                                                                | 13,692,000us-gaap_InterestIncomeExpenseNet/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_AllOtherSegmentsMember                                                                                                                                                              | (9,162,000)us-gaap_InterestIncomeExpenseNet/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_AllOtherSegmentsMember                                                                                                                                                              |   |
| Total non-interest income                                                          | 22,386,000us-gaap_NoninterestIncome/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_AllOtherSegmentsMember                                                                                                                                                                     | 28,363,000us-gaap_NoninterestIncome/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_AllOtherSegmentsMember                                                                                                                                                                      |   |
| Provision for credit losses                                                        | 31,019,000us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_AllOtherSegmentsMember                                                                                                                                                   | (16,309,000)us-gaap_ProvisionForLoanLeaseAndOtherLosses/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_AllOtherSegmentsMember                                                                                                                                                  |   |
| Total expenses                                                                     | 111,134,000sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_AllOtherSegmentsMember                                                                                                                                                 | 123,227,000sov_GeneralAndAdministrativeAndOtherExpenses/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_AllOtherSegmentsMember                                                                                                                                                  |   |
| Income/(loss) before income taxes                                                  | (106,075,000)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_AllOtherSegmentsMember                                                                                        | (87,717,000)us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_AllOtherSegmentsMember                                                                                          |   |
| Intersegment (expense)/revenue                                                     | 21,170,000us-gaap_Revenues/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_AllOtherSegmentsMember                                                                                                                                                                              | 32,319,000us-gaap_Revenues/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_AllOtherSegmentsMember                                                                                                                                                                               |   |
| Total average assets                                                               | $ 29,180,879,000sov_SegmentReportingInformationAverageAssets1/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_AllOtherSegmentsMember                                                                                                                                           | $ 26,529,244,000sov_SegmentReportingInformationAverageAssets1/ us-gaap_StatementBusinessSegmentsAxis= us-gaap_AllOtherSegmentsMember                                                                                                                                            |   |

| X                                                                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fees and Other Income Including Realized Gains (Losses) on Sale of Investment Securities
+ References
No definition available.
+ Details**Name:**sov_FeesandOtherIncomeIncludingRealizedGainsLossesonSaleofInvestmentSecurities**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                    |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Gain on Change in Control
+ References
No definition available.
+ Details**Name:**sov_GainonChangeinControl**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
General and administrative and other expenses
+ References
No definition available.
+ Details**Name:**sov_GeneralAndAdministrativeAndOtherExpenses**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Minimum Annual Revenue to Service Corporation
+ References
No definition available.
+ Details**Name:**sov_MinimumAnnualRevenuetoServiceCorporation**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of average assets attributed to the reportable segment.
+ References
No definition available.
+ Details**Name:**sov_SegmentReportingInformationAverageAssets1**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.
+ References
No definition available.
+ Details**Name:**us-gaap_DebtInstrumentTerm**Namespace Prefix:**us-gaap_**Data Type:**xbrli:durationItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 20 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35710027&loc=d3e41242-110953Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 10 -Article 5
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The net amount of operating interest income (expense).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.10) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 10 -Article 9
+ Details**Name:**us-gaap_InterestIncomeExpenseNet**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The total amount of noninterest income which may be derived from: (1) fees and commissions; (2) premiums earned; (3) insurance policy charges; (4) the sale or disposal of assets; and (5) other sources not otherwise specified.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.13) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 13 -Article 9
+ Details**Name:**us-gaap_NoninterestIncome**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 11 -Article 9Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.11) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 11B -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953423-111524
+ Details**Name:**us-gaap_ProvisionForLoanLeaseAndOtherLosses**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.1) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Article 5
+ Details**Name:**us-gaap_Revenues**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------|
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| X                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_LineOfCreditFacilityAxis=sov_ChryslerGroupMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                            |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=sov_ScusaMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------|
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