| **STOCK-BASED COMPENSATION (SCUSA Compensation Plan - Narrative) (Details) (USD $)**                        | 12 Months Ended                                                                                                                                                                                                                                | 0 Months Ended                                                                                                                                                                                                                  | 11 Months Ended                                                                                                                              | 12 Months Ended                                                                                                                                                                                                                                |                                                                                                                                                                                                                    |                                                                                                                                                                                                        |
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| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Stock vesting period                                                                                        | 3 years                                                                                                                                                                                                                                        |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Compensation not yet recognized, stock options                                                              | $ 59,500,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions                                                                                                                      |                                                                                                                                                                                                                            |                                                                                                                                         | $ 59,500,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions                                                                                                                      |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Stock Options [Member]                                                                                      |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Compensation not yet recognized, period for recognition                                                     | 2 years 3 months 18 days                                                                                                                                                                                                                       |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| SCUSA [Member]                                                                                              |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Common stock , shares issued                                                                                |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            | 85,242,042us-gaap_CommonStockSharesIssued/ dei_LegalEntityAxis= sov_ScusaMember                                                              |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Common stock , par value (in usd per share)                                                                 |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            | $ 24.00us-gaap_CommonStockParOrStatedValuePerShare/ dei_LegalEntityAxis= sov_ScusaMember                                                     |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Proceeds from IPO                                                                                           |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            | 0us-gaap_ProceedsFromIssuanceInitialPublicOffering/ dei_LegalEntityAxis= sov_ScusaMember                                                     |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Stock compensation expense                                                                                  |                                                                                                                                                                                                                                           | 82,600,000us-gaap_AllocatedShareBasedCompensationExpense/ dei_LegalEntityAxis= sov_ScusaMember                                                                                                                                  | 117,800,000us-gaap_AllocatedShareBasedCompensationExpense/ dei_LegalEntityAxis= sov_ScusaMember                                              | 99,600,000us-gaap_AllocatedShareBasedCompensationExpense/ dei_LegalEntityAxis= sov_ScusaMember                                                                                                                                                 |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Accelerated vesting cost for certain executives                                                             |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            | 33,800,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAcceleratedCompensationCost/ dei_LegalEntityAxis= sov_ScusaMember |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Additional stock options granted (in shares)                                                                | 1,731,329us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross/ dei_LegalEntityAxis= sov_ScusaMember                                                                                                     |                                                                                                                                                                                                                            | 1,406,835us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross/ dei_LegalEntityAxis= sov_ScusaMember   |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Fair value of options granted in period                                                                     | 2,500,000sov_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsGrantedinPeriodFairValue/ dei_LegalEntityAxis= sov_ScusaMember                                                                                                    |                                                                                                                                                                                                                            | 10,200,000sov_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsGrantedinPeriodFairValue/ dei_LegalEntityAxis= sov_ScusaMember |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Total number of stock options outstanding (in shares)                                                       | 21,357,911us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber/ dei_LegalEntityAxis= sov_ScusaMember                                                                                                      |                                                                                                                                                                                                                            | 25,400,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber/ dei_LegalEntityAxis= sov_ScusaMember    | 21,357,911us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber/ dei_LegalEntityAxis= sov_ScusaMember                                                                                                      |                                                                                                                                                                                                               | 23,910,062us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber/ dei_LegalEntityAxis= sov_ScusaMember                                                              |   |
| Stock options awards outstanding, fair value                                                                | 187,637,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue/ dei_LegalEntityAxis= sov_ScusaMember                                                                                             | 369,300,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue/ dei_LegalEntityAxis= sov_ScusaMember                                                                              |                                                                                                                                         | 187,637,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue/ dei_LegalEntityAxis= sov_ScusaMember                                                                                             |                                                                                                                                                                                                               | 267,634,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue/ dei_LegalEntityAxis= sov_ScusaMember                                                     |   |
| Fair value of additional stock option grant                                                                 |                                                                                                                                                                                                                                           | 15,000,000sov_SharebasedCompensationArrangementbySharebasedPaymentAwardOptionsAdditionalSharesGrantedIntrinsicValue/ dei_LegalEntityAxis= sov_ScusaMember                                                                       |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Compensation not yet recognized, stock options                                                              | 22,800,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions/ dei_LegalEntityAxis= sov_ScusaMember                                                                                  |                                                                                                                                                                                                                            |                                                                                                                                         | 22,800,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions/ dei_LegalEntityAxis= sov_ScusaMember                                                                                  |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| SCUSA [Member] | Stock Options [Member]                                                                     |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Compensation not yet recognized, period for recognition                                                     | 2 years 3 months 18 days                                                                                                                                                                                                                       |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| SCUSA [Member] | Employees [Member]                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Stock vesting period                                                                                        |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            | 5 years                                                                                                                                      |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| SCUSA [Member] | Director [Member]                                                                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Stock vesting period                                                                                        |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            | 3 years                                                                                                                                      |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| SCUSA [Member] | Omnibus Incentive Plan [Member]                                                            |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Common shares stock awards available for grant                                                              |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   | 583,890us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= sov_OmnibusIncentivePlanMember |
| Stock vesting period                                                                                        | 5 years                                                                                                                                                                                                                                        |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Employee benefits and share-based compensation                                                              | 2,500,000us-gaap_EmployeeBenefitsAndShareBasedCompensation/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= sov_OmnibusIncentivePlanMember                                                                                         |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| SCUSA [Member] | Omnibus Incentive Plan [Member] | Stock Options [Member]                                   |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Expiration period                                                                                           | 10 years                                                                                                                                                                                                                                       |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| SCUSA [Member] | Stock-Based Compensation Plan [Member] | Cycle One, July 2007 through June 2009 [Member]   |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Maximum authorized shares                                                                                   | 96,030us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized/ us-gaap_AwardDateAxis= sov_CycleOneMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember    |                                                                                                                                                                                                                            |                                                                                                                                         | 96,030us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized/ us-gaap_AwardDateAxis= sov_CycleOneMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember    |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Price per share (in usd per share)                                                                          | $ 19.38us-gaap_SharePrice/ us-gaap_AwardDateAxis= sov_CycleOneMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember                                                                          |                                                                                                                                                                                                                            |                                                                                                                                         | $ 19.38us-gaap_SharePrice/ us-gaap_AwardDateAxis= sov_CycleOneMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember                                                                          |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Number of shares distributed                                                                                | 77,469sov_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofSharesDistributed/ us-gaap_AwardDateAxis= sov_CycleOneMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember       |                                                                                                                                                                                                                            |                                                                                                                                         | 77,469sov_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofSharesDistributed/ us-gaap_AwardDateAxis= sov_CycleOneMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember       |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| SCUSA [Member] | Stock-Based Compensation Plan [Member] | Cycle Two, July 2007 through June 2010 [Member]   |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Maximum authorized shares                                                                                   | 144,120us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized/ us-gaap_AwardDateAxis= sov_CycleTwoMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember   |                                                                                                                                                                                                                            |                                                                                                                                         | 144,120us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized/ us-gaap_AwardDateAxis= sov_CycleTwoMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember   |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Price per share (in usd per share)                                                                          | $ 19.38us-gaap_SharePrice/ us-gaap_AwardDateAxis= sov_CycleTwoMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember                                                                          |                                                                                                                                                                                                                            |                                                                                                                                         | $ 19.38us-gaap_SharePrice/ us-gaap_AwardDateAxis= sov_CycleTwoMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember                                                                          |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Number of shares distributed                                                                                | 114,040sov_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofSharesDistributed/ us-gaap_AwardDateAxis= sov_CycleTwoMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember      |                                                                                                                                                                                                                            |                                                                                                                                         | 114,040sov_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofSharesDistributed/ us-gaap_AwardDateAxis= sov_CycleTwoMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember      |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| SCUSA [Member] | Stock-Based Compensation Plan [Member] | Cycle Three, July 2008 through June 2011 [Member] |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Maximum authorized shares                                                                                   | 147,908us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized/ us-gaap_AwardDateAxis= sov_CycleThreeMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember |                                                                                                                                                                                                                            |                                                                                                                                         | 147,908us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized/ us-gaap_AwardDateAxis= sov_CycleThreeMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Price per share (in usd per share)                                                                          | $ 7.29us-gaap_SharePrice/ us-gaap_AwardDateAxis= sov_CycleThreeMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember                                                                         |                                                                                                                                                                                                                            |                                                                                                                                         | $ 7.29us-gaap_SharePrice/ us-gaap_AwardDateAxis= sov_CycleThreeMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember                                                                         |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Number of shares distributed                                                                                | 120,732sov_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofSharesDistributed/ us-gaap_AwardDateAxis= sov_CycleThreeMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember    |                                                                                                                                                                                                                            |                                                                                                                                         | 120,732sov_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofSharesDistributed/ us-gaap_AwardDateAxis= sov_CycleThreeMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember    |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| SCUSA [Member] | Stock-Based Compensation Plan [Member] | Cycle Four, July 2009 through June 2012 [Member]  |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Maximum authorized shares                                                                                   | 157,611us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized/ us-gaap_AwardDateAxis= sov_CycleFourMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember  |                                                                                                                                                                                                                            |                                                                                                                                         | 157,611us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized/ us-gaap_AwardDateAxis= sov_CycleFourMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember  |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Price per share (in usd per share)                                                                          | $ 6.50us-gaap_SharePrice/ us-gaap_AwardDateAxis= sov_CycleFourMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember                                                                          |                                                                                                                                                                                                                            |                                                                                                                                         | $ 6.50us-gaap_SharePrice/ us-gaap_AwardDateAxis= sov_CycleFourMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember                                                                          |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Number of shares distributed                                                                                | 43,475sov_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofSharesDistributed/ us-gaap_AwardDateAxis= sov_CycleFourMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember      |                                                                                                                                                                                                                            |                                                                                                                                         | 43,475sov_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofSharesDistributed/ us-gaap_AwardDateAxis= sov_CycleFourMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember      |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| SCUSA [Member] | Stock-Based Compensation Plan [Member] | Cycle Five, July 2010 through June 2013 [Member]  |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Maximum authorized shares                                                                                   | 163,302us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized/ us-gaap_AwardDateAxis= sov_CycleFiveMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember  |                                                                                                                                                                                                                            |                                                                                                                                         | 163,302us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized/ us-gaap_AwardDateAxis= sov_CycleFiveMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember  |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Price per share (in usd per share)                                                                          | $ 6.87us-gaap_SharePrice/ us-gaap_AwardDateAxis= sov_CycleFiveMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember                                                                          |                                                                                                                                                                                                                            |                                                                                                                                         | $ 6.87us-gaap_SharePrice/ us-gaap_AwardDateAxis= sov_CycleFiveMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember                                                                          |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Number of shares distributed                                                                                | 0sov_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofSharesDistributed/ us-gaap_AwardDateAxis= sov_CycleFiveMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember           |                                                                                                                                                                                                                            |                                                                                                                                         | 0sov_SharebasedCompensationArrangementbySharebasedPaymentAwardNumberofSharesDistributed/ us-gaap_AwardDateAxis= sov_CycleFiveMember/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= us-gaap_StockCompensationPlanMember           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Common Stock [Member] | SCUSA [Member]                                                                      |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Common shares stock awards available for grant                                                              |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           | 29,400,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_StatementEquityComponentsAxis= us-gaap_CommonStockMember |                                                                                                                                                                                                   |   |
| Percentage of equity invested in the Company for the stock awards available for grant                       |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           | 8.50%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOfOutstandingStockMaximum/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_StatementEquityComponentsAxis= us-gaap_CommonStockMember  |                                                                                                                                                                                                   |   |
| Common Stock [Member] | SCUSA [Member] | Omnibus Incentive Plan [Member]                                    |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Common stock , shares issued                                                                                |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               | 5,192,640us-gaap_CommonStockSharesIssued/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_PlanNameAxis= sov_OmnibusIncentivePlanMember/ us-gaap_StatementEquityComponentsAxis= us-gaap_CommonStockMember |   |
| Noncontrolling Interest [Member] | SCUSA [Member]                                                           |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Stock options awards outstanding, fair value                                                                |                                                                                                                                                                                                                                           | 210,200,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue/ dei_LegalEntityAxis= sov_ScusaMember/ us-gaap_StatementEquityComponentsAxis= us-gaap_NoncontrollingInterestMember |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Stock Compensation Expense [Member] | SCUSA [Member]                                                        |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**                          |                                                                                                                                                                                                                                           |                                                                                                                                                                                                                            |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |
| Stock options awards outstanding, fair value                                                                |                                                                                                                                                                                                                                           | $ 159,100,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue/ us-gaap_IncomeStatementLocationAxis= sov_StockCompensationExpenseMember/ dei_LegalEntityAxis= sov_ScusaMember   |                                                                                                                                         |                                                                                                                                                                                                                                           |                                                                                                                                                                                                               |                                                                                                                                                                                                   |   |

| X                                                                                                                                                                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Distributed
+ References
No definition available.
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| - Definition
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Shares Granted, Intrinsic Value
+ References
No definition available.
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| - Definition
Share-based Compensation Arrangement by Share-based Payment Award, Options, Granted in Period, Fair Value
+ References
No definition available.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Face amount or stated value per share of common stock.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Costs and payments related to employee benefits and equity-based compensation, such as pension expense and contributions, other postretirement benefits expense and payments, stock or unit options expense, and amortization of restricted stock or unit.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Unrecognized cost of unvested options awarded to employees as compensation.
+ References
No definition available.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The cash inflow associated with the amount received from entity's first offering of stock to the public.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Additional share-based compensation cost recognized as a result of an occurrence of an event that accelerates its recognition.
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).
+ References
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Gross number of share options (or share units) granted during the period.
+ References
No definition available.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Number of options outstanding, including both vested and non-vested options.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Maximum number of shares that may be issued in accordance with the plan as a proportion of outstanding capital stock.
+ References
No definition available.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Price of a single share of a number of saleable stocks of a company.
+ References
No definition available.
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