| **FAIR VALUE (Quantitative Information) (Details) (USD $)**                                                                                                   | 12 Months Ended                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                  |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
||
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Available-for-sale at fair value                                                                                                                              | 15,908,078,000us-gaap_AvailableForSaleSecurities                                                                                                                                                                                                                                                                                                                                                                                     | $ 11,646,240,000us-gaap_AvailableForSaleSecurities                                                                                                                                                                                                                                               |
| Retail installment contracts held for investment                                                                                                              | 845,911,000us-gaap_LoansReceivableFairValueDisclosure                                                                                                                                                                                                                                                                                                                                                                                | 0us-gaap_LoansReceivableFairValueDisclosure                                                                                                                                                                                                                                                      |
| Mortgage servicing rights                                                                                                                                     | 145,047,000us-gaap_ServicingAssetAtFairValueAmount                                                                                                                                                                                                                                                                                                                                                                                   | 141,787,000us-gaap_ServicingAssetAtFairValueAmount                                                                                                                                                                                                                                               |
| Derivative assets at fair value                                                                                                                               | 366,061,000us-gaap_DerivativeAssets                                                                                                                                                                                                                                                                                                                                                                                                  | 222,491,000us-gaap_DerivativeAssets                                                                                                                                                                                                                                                              |
| Level 3 [Member]                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Available-for-sale at fair value                                                                                                                              | 1,267,643,000us-gaap_AvailableForSaleSecurities/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                                                                                                                                                                                                                                                                                                 | 52,940,000us-gaap_AvailableForSaleSecurities/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                                                                                                                                                                |
| Mortgage servicing rights                                                                                                                                     | 145,047,000us-gaap_ServicingAssetAtFairValueAmount/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                                                                                                                                                                                                                                                                                              | 141,787,000us-gaap_ServicingAssetAtFairValueAmount/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                                                                                                                                                          |
| Derivative assets at fair value                                                                                                                               | 3,070,000us-gaap_DerivativeAssets/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                                                                                                                                                                                                                                                                                                               | 561,000us-gaap_DerivativeAssets/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member                                                                                                                                                                             |
| Recurring [Member]                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Available-for-sale at fair value                                                                                                                              | 15,908,078,000us-gaap_AvailableForSaleSecurities/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember                                                                                                                                                                                                                                                                                          | 11,646,240,000us-gaap_AvailableForSaleSecurities/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember                                                                                                                                                      |
| Retail installment contracts held for investment                                                                                                              | 845,911,000us-gaap_LoansReceivableFairValueDisclosure/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                             |
| Mortgage servicing rights                                                                                                                                     | 145,047,000us-gaap_ServicingAssetAtFairValueAmount/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember                                                                                                                                                                                                                                                                                        | 141,787,000us-gaap_ServicingAssetAtFairValueAmount/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember                                                                                                                                                    |
| Recurring [Member] | Mortgage banking interest rate lock commitments [Member]                                                                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Derivative assets at fair value                                                                                                                               | 3,063,000us-gaap_DerivativeAssets/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateLockCommitmentsMember/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember                                                                                                                                                                                                                        | 547,000us-gaap_DerivativeAssets/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateLockCommitmentsMember/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember                                                                                      |
| Recurring [Member] | Level 3 [Member]                                                                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Available-for-sale at fair value                                                                                                                              | 1,267,643,000us-gaap_AvailableForSaleSecurities/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember                                                                                                                                                                                                      | 52,940,000us-gaap_AvailableForSaleSecurities/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember                                                                     |
| Retail installment contracts held for investment                                                                                                              | 845,911,000us-gaap_LoansReceivableFairValueDisclosure/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                             |
| Mortgage servicing rights                                                                                                                                     | 145,047,000us-gaap_ServicingAssetAtFairValueAmount/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember                                                                                                                                                                                                   | 141,787,000us-gaap_ServicingAssetAtFairValueAmount/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember                                                               |
| Recurring [Member] | Level 3 [Member] | Discounted Cash Flow [Member]                                                                                         |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Prepayment rate (CPR)                                                                                                                                         | 11.00%us-gaap_FairValueInputsPrepaymentRate/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember                                                                                                                                            |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Mortgage banking interest rate lock commitments [Member]                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Derivative assets at fair value                                                                                                                               | 3,063,000us-gaap_DerivativeAssets/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateLockCommitmentsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember                                                                                                                                   | 547,000us-gaap_DerivativeAssets/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateLockCommitmentsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember |
| Recurring [Member] | Level 3 [Member] | Mortgage banking interest rate lock commitments [Member] | Discounted Cash Flow [Member]                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Derivative assets at fair value                                                                                                                               | 3,063,000us-gaap_DerivativeAssets/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateLockCommitmentsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember                                                                     |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Pull through percentage                                                                                                                                       | 76.27%sov_FairValueInputsPullThroughRate/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateLockCommitmentsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember                                                              |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Mortgage banking interest rate lock commitments [Member] | Discounted Cash Flow [Member] | Minimum [Member]           |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| MSR value                                                                                                                                                     | 0.68%sov_FairValueInputsMortgageServicingRightValue/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateLockCommitmentsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_MinimumMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember         |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Mortgage banking interest rate lock commitments [Member] | Discounted Cash Flow [Member] | Maximum [Member]           |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| MSR value                                                                                                                                                     | 1.06%sov_FairValueInputsMortgageServicingRightValue/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateLockCommitmentsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_MaximumMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember         |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Mortgage banking interest rate lock commitments [Member] | Discounted Cash Flow [Member] | Weighted average [Member]  |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| MSR value                                                                                                                                                     | 0.99%sov_FairValueInputsMortgageServicingRightValue/ us-gaap_DerivativeInstrumentRiskAxis= us-gaap_InterestRateLockCommitmentsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_WeightedAverageMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Financing bonds [Member] | Discounted Cash Flow [Member]                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Available-for-sale at fair value                                                                                                                              | 1,215,997,000us-gaap_AvailableForSaleSecurities/ us-gaap_FairValueByAssetClassAxis= us-gaap_BondsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember                                                                                |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Financing bonds [Member] | Discounted Cash Flow [Member] | Minimum [Member]                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Discount rate                                                                                                                                                 | 0.80%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByAssetClassAxis= us-gaap_BondsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_MinimumMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember                                             |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Financing bonds [Member] | Discounted Cash Flow [Member] | Maximum [Member]                                           |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Discount rate                                                                                                                                                 | 2.07%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByAssetClassAxis= us-gaap_BondsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_MaximumMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember                                             |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Financing bonds [Member] | Discounted Cash Flow [Member] | Weighted average [Member]                                  |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Discount rate                                                                                                                                                 | 1.27%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByAssetClassAxis= us-gaap_BondsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_WeightedAverageMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember                                     |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Sale-leaseback securities [Member] | Consensus Pricing [Member]                                                       |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Available-for-sale at fair value                                                                                                                              | 51,646,000us-gaap_AvailableForSaleSecurities/ us-gaap_FairValueByAssetClassAxis= sov_SaleLeasebackSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_ValuationTechniqueAxis= sov_ConsensusPricingMember                                                                       |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Offered quotes                                                                                                                                                | 130.85%sov_FairValueInputsOfferedQuotesAsPercentageOfFaceValue/ us-gaap_FairValueByAssetClassAxis= sov_SaleLeasebackSecuritiesMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_ValuationTechniqueAxis= sov_ConsensusPricingMember                                                     |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Retail installment contracts held for investment [Member] | Discounted Cash Flow [Member]                             |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Retail installment contracts held for investment                                                                                                              | 845,911,000us-gaap_LoansReceivableFairValueDisclosure/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember                                        |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| ABS                                                                                                                                                           | 0.40%sov_FairValueInputsABSRate/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember                                                              |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Retail installment contracts held for investment [Member] | Discounted Cash Flow [Member] | Minimum [Member]          |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Discount rate                                                                                                                                                 | 5.55%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_MinimumMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember           |                                                                                                                                                                                                                                                                                             |
| Recovery rate                                                                                                                                                 | 25.00%sov_FairValueInputsRecoveryRate/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_MinimumMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember              |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Retail installment contracts held for investment [Member] | Discounted Cash Flow [Member] | Maximum [Member]          |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Discount rate                                                                                                                                                 | 12.00%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_MaximumMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember          |                                                                                                                                                                                                                                                                                             |
| Recovery rate                                                                                                                                                 | 45.00%sov_FairValueInputsRecoveryRate/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_MaximumMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember              |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Retail installment contracts held for investment [Member] | Discounted Cash Flow [Member] | Weighted average [Member] |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Discount rate                                                                                                                                                 | 8.87%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_WeightedAverageMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember   |                                                                                                                                                                                                                                                                                             |
| Recovery rate                                                                                                                                                 | 38.40%sov_FairValueInputsRecoveryRate/ us-gaap_FairValueByAssetClassAxis= sov_RetailInstallmentContractsHeldforinvestmentMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_WeightedAverageMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember      |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Mortgage servicing rights [Member] | Discounted Cash Flow [Member]                                                    |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                          |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Mortgage servicing rights                                                                                                                                     | 145,047,000us-gaap_ServicingAssetAtFairValueAmount/ us-gaap_FairValueByAssetClassAxis= sov_ServicingAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember                                                                       |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Discount rate                                                                                                                                                 | 10.10%us-gaap_FairValueInputsDiscountRate/ us-gaap_FairValueByAssetClassAxis= sov_ServicingAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember                                                                                |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Mortgage servicing rights [Member] | Discounted Cash Flow [Member] | Minimum [Member]                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Prepayment rate (CPR)                                                                                                                                         | 0.67%us-gaap_FairValueInputsPrepaymentRate/ us-gaap_FairValueByAssetClassAxis= sov_ServicingAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_MinimumMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember                                     |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Mortgage servicing rights [Member] | Discounted Cash Flow [Member] | Maximum [Member]                                 |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Prepayment rate (CPR)                                                                                                                                         | 41.19%us-gaap_FairValueInputsPrepaymentRate/ us-gaap_FairValueByAssetClassAxis= sov_ServicingAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_MaximumMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember                                    |                                                                                                                                                                                                                                                                                             |
| Recurring [Member] | Level 3 [Member] | Mortgage servicing rights [Member] | Discounted Cash Flow [Member] | Weighted average [Member]                        |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| **Fair Value Inputs [Abstract]**                                                                                                                              |                                                                                                                                                                                                                                                                                                                                                                                                                                 |                                                                                                                                                                                                                                                                                             |
| Prepayment rate (CPR)                                                                                                                                         | 10.51%us-gaap_FairValueInputsPrepaymentRate/ us-gaap_FairValueByAssetClassAxis= sov_ServicingAssetsMember/ us-gaap_FairValueByFairValueHierarchyLevelAxis= us-gaap_FairValueInputsLevel3Member/ us-gaap_FairValueByMeasurementFrequencyAxis= us-gaap_FairValueMeasurementsRecurringMember/ us-gaap_RangeAxis= us-gaap_WeightedAverageMember/ us-gaap_ValuationTechniqueAxis= sov_DiscountedCashFlowMember                            |                                                                                                                                                                                                                                                                                             |

| X                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair Value Inputs, ABS Rate
+ References
No definition available.
+ Details**Name:**sov_FairValueInputsABSRate**Namespace Prefix:**sov_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                  |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Estimated value of the servicing right embedded in the underlying loan, expressed in basis points of outstanding unpaid principal balance
+ References
No definition available.
+ Details**Name:**sov_FairValueInputsMortgageServicingRightValue**Namespace Prefix:**sov_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Price at which a dealer is willing to buy an instrument, used as an input to measure fair value.
+ References
No definition available.
+ Details**Name:**sov_FairValueInputsOfferedQuotesAsPercentageOfFaceValue**Namespace Prefix:**sov_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair Value Inputs, Pull-through Rate
+ References
No definition available.
+ Details**Name:**sov_FairValueInputsPullThroughRate**Namespace Prefix:**sov_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                          |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair Value Inputs, Recovery Rate
+ References
No definition available.
+ Details**Name:**sov_FairValueInputsRecoveryRate**Namespace Prefix:**sov_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562
+ Details**Name:**us-gaap_AvailableForSaleSecurities**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13495-108611Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=34720828&loc=SL20225862-175312Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 45 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41271-113958Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 20 -Section 55 -Paragraph 10 -URI http://asc.fasb.org/extlink&oid=36459792&loc=SL20226008-175313
+ Details**Name:**us-gaap_DerivativeAssets**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueInputsAbstract**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                         |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueInputsAssetsQuantitativeInformationLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value.  For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258
+ Details**Name:**us-gaap_FairValueInputsDiscountRate**Namespace Prefix:**us-gaap_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Rate at which loans or a loan portfolio are expected to prepay principal balances, used as an input to measure fair value.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (bbb) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258
+ Details**Name:**us-gaap_FairValueInputsPrepaymentRate**Namespace Prefix:**us-gaap_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Glossary Loan -URI http://asc.fasb.org/extlink&oid=6517073
+ Details**Name:**us-gaap_LoansReceivableFairValueDisclosure**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=7882072&loc=d3e122625-111746
+ Details**Name:**us-gaap_ServicingAssetAtFairValueAmount**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |