|**LOANS AND ALLOWANCE FOR CREDIT LOSSES (Consumer Lending Asset Quality Indicators-Credit Score) (Details) (USD $)In Thousands, unless otherwise specified**                                                                                                                                                                                                                                                                                                                                                                | Mar. 31, 2015                                                                                                                                                                                                                                                                                                                | Dec. 31, 2014                                                                                                                                                                                                                                                                                                               
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|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | $ 78,520,165us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome                                                                                                                                                                                                                                                              | [1],[2]                                                                                                                                                                                                                                                                                                                     
|Retail installment contracts and auto loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 24,405,668us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember                                                                                                                             |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Retail installment contracts and auto loans                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 100.00%sov_PercentageofTotalLoansRetailInstallmentContractsandAutoLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember                                                                                                                   |                                                                                                                                                                                                                                                                                                                             
|Retail installment contracts and auto loans [Member] | FICO score less than 600 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 12,648,832us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreLessthan600Member                                                       |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Retail installment contracts and auto loans                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 51.80%sov_PercentageofTotalLoansRetailInstallmentContractsandAutoLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreLessthan600Member                                              |                                                                                                                                                                                                                                                                                                                             
|Retail installment contracts and auto loans [Member] | FICO score of 600 to 639 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 5,221,963us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof600to639Member                                                         |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Retail installment contracts and auto loans                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 21.40%sov_PercentageofTotalLoansRetailInstallmentContractsandAutoLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof600to639Member                                               |                                                                                                                                                                                                                                                                                                                             
|Retail installment contracts and auto loans [Member] | FICO score of 640 to 679 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 2,429,771us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof640to679Member                                                         |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Retail installment contracts and auto loans                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 10.00%sov_PercentageofTotalLoansRetailInstallmentContractsandAutoLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof640to679Member                                               |                                                                                                                                                                                                                                                                                                                             
|Retail installment contracts and auto loans [Member] | FICO score of 680 to 719 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 0us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof680to719Member                                                                 |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Retail installment contracts and auto loans                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 0.00%sov_PercentageofTotalLoansRetailInstallmentContractsandAutoLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof680to719Member                                                |                                                                                                                                                                                                                                                                                                                             
|Retail installment contracts and auto loans [Member] | FICO score of 720 to 759 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 0us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof720to759Member                                                                 |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Retail installment contracts and auto loans                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 0.00%sov_PercentageofTotalLoansRetailInstallmentContractsandAutoLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof720to759Member                                                |                                                                                                                                                                                                                                                                                                                             
|Retail installment contracts and auto loans [Member] | FICO score equal to or greater than 760 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 0us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreEqualtoorGreaterthan760Member                                                    |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Retail installment contracts and auto loans                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 0.00%sov_PercentageofTotalLoansRetailInstallmentContractsandAutoLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreEqualtoorGreaterthan760Member                                   |                                                                                                                                                                                                                                                                                                                             
|Retail installment contracts and auto loans [Member] | FICO score not refreshed [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 4,105,102us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_InternalCreditAssessmentAxis= sov_FicoScoreNotRefreshedMember                                                       |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Retail installment contracts and auto loans                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 16.80%sov_PercentageofTotalLoansRetailInstallmentContractsandAutoLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_InternalCreditAssessmentAxis= sov_FicoScoreNotRefreshedMember                                             |                                                                                                                                                                                                                                                                                                                             
|Personal unsecured loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 2,696,815us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember                                                                                                                                                 |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Personal unsecured loans balance                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 100.00%sov_PercentageofTotalLoansPersonalUnsecuredLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                             
|Personal unsecured loans [Member] | FICO score less than 600 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 472,501us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreLessthan600Member                                                                             |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Personal unsecured loans balance                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 17.50%sov_PercentageofTotalLoansPersonalUnsecuredLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreLessthan600Member                                                                                 |                                                                                                                                                                                                                                                                                                                             
|Personal unsecured loans [Member] | FICO score of 600 to 639 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 439,314us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof600to639Member                                                                              |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Personal unsecured loans balance                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 16.30%sov_PercentageofTotalLoansPersonalUnsecuredLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof600to639Member                                                                                  |                                                                                                                                                                                                                                                                                                                             
|Personal unsecured loans [Member] | FICO score of 640 to 679 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 1,189,155us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof640to679Member                                                                            |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Personal unsecured loans balance                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 44.10%sov_PercentageofTotalLoansPersonalUnsecuredLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof640to679Member                                                                                  |                                                                                                                                                                                                                                                                                                                             
|Personal unsecured loans [Member] | FICO score of 680 to 719 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 64,417us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof680to719Member                                                                               |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Personal unsecured loans balance                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 2.40%sov_PercentageofTotalLoansPersonalUnsecuredLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof680to719Member                                                                                   |                                                                                                                                                                                                                                                                                                                             
|Personal unsecured loans [Member] | FICO score of 720 to 759 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 72,614us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof720to759Member                                                                               |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Personal unsecured loans balance                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 2.70%sov_PercentageofTotalLoansPersonalUnsecuredLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof720to759Member                                                                                   |                                                                                                                                                                                                                                                                                                                             
|Personal unsecured loans [Member] | FICO score equal to or greater than 760 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 76,368us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreEqualtoorGreaterthan760Member                                                                  |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Personal unsecured loans balance                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 2.80%sov_PercentageofTotalLoansPersonalUnsecuredLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreEqualtoorGreaterthan760Member                                                                      |                                                                                                                                                                                                                                                                                                                             
|Personal unsecured loans [Member] | FICO score not refreshed [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 382,446us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_InternalCreditAssessmentAxis= sov_FicoScoreNotRefreshedMember                                                                            |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Personal unsecured loans balance                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 14.20%sov_PercentageofTotalLoansPersonalUnsecuredLoans/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_InternalCreditAssessmentAxis= sov_FicoScoreNotRefreshedMember                                                                                |                                                                                                                                                                                                                                                                                                                             
|Home equity loans and lines of credit [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 6,171,981us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                                                                                                                                                        |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Home equity loans and lines                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 100.00%sov_PercentageofTotalLoansHomeEquityLoansandLines/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember                                                                                                                                                            |                                                                                                                                                                                                                                                                                                                             
|Home equity loans and lines of credit [Member] | FICO score less than 600 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 304,669us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreLessthan600Member                                                                                    |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Home equity loans and lines                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 4.90%sov_PercentageofTotalLoansHomeEquityLoansandLines/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreLessthan600Member                                                                                        |                                                                                                                                                                                                                                                                                                                             
|Home equity loans and lines of credit [Member] | FICO score of 600 to 639 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 283,304us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof600to639Member                                                                                     |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Home equity loans and lines                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 4.60%sov_PercentageofTotalLoansHomeEquityLoansandLines/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof600to639Member                                                                                         |                                                                                                                                                                                                                                                                                                                             
|Home equity loans and lines of credit [Member] | FICO score of 640 to 679 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 509,672us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof640to679Member                                                                                     |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Home equity loans and lines                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 8.30%sov_PercentageofTotalLoansHomeEquityLoansandLines/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof640to679Member                                                                                         |                                                                                                                                                                                                                                                                                                                             
|Home equity loans and lines of credit [Member] | FICO score of 680 to 719 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 856,525us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof680to719Member                                                                                     |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Home equity loans and lines                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 13.90%sov_PercentageofTotalLoansHomeEquityLoansandLines/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof680to719Member                                                                                        |                                                                                                                                                                                                                                                                                                                             
|Home equity loans and lines of credit [Member] | FICO score of 720 to 759 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 1,193,212us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof720to759Member                                                                                   |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Home equity loans and lines                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 19.30%sov_PercentageofTotalLoansHomeEquityLoansandLines/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreof720to759Member                                                                                        |                                                                                                                                                                                                                                                                                                                             
|Home equity loans and lines of credit [Member] | FICO score equal to or greater than 760 [Member]                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 2,816,648us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreEqualtoorGreaterthan760Member                                                                      |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Home equity loans and lines                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 45.60%sov_PercentageofTotalLoansHomeEquityLoansandLines/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember/ us-gaap_InternalCreditAssessmentAxis= sov_FICOScoreEqualtoorGreaterthan760Member                                                                           |                                                                                                                                                                                                                                                                                                                             
|Home equity loans and lines of credit [Member] | FICO score not refreshed [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|**Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                             
|Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | $ 207,951us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember/ us-gaap_InternalCreditAssessmentAxis= sov_FicoScoreNotRefreshedMember                                                                                 |                                                                                                                                                                                                                                                                                                                             
|Percentage of total loans, Home equity loans and lines                                                                                                                                                                                                                                                                                                                                                                                                                                                                      | 3.40%sov_PercentageofTotalLoansHomeEquityLoansandLines/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_HomeEquityMember/ us-gaap_InternalCreditAssessmentAxis= sov_FicoScoreNotRefreshedMember                                                                                       |                                                                                                                                                                                                                                                                                                                             
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           
|[1]
              The Company has interests in certain securitization trusts ("Trusts") that are considered variable interest entities ("VIEs") for accounting purposes. The Company consolidates VIEs where it is deemed the primary beneficiary. See Note 7 to these Condensed Consolidated Financial Statements for additional information.[2]
              Loans held for investment includes $676.1 million and $845.9 million of loans recorded at fair value at March 31, 2015 and December 31, 2014, respectively. | [1]                                                                                                                                                                                                                                                                                                                          | The Company has interests in certain securitization trusts ("Trusts") that are considered variable interest entities ("VIEs") for accounting purposes. The Company consolidates VIEs where it is deemed the primary beneficiary. See Note 7 to these Condensed Consolidated Financial Statements for additional information.
|[1]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | The Company has interests in certain securitization trusts ("Trusts") that are considered variable interest entities ("VIEs") for accounting purposes. The Company consolidates VIEs where it is deemed the primary beneficiary. See Note 7 to these Condensed Consolidated Financial Statements for additional information.
|[2]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | Loans held for investment includes $676.1 million and $845.9 million of loans recorded at fair value at March 31, 2015 and December 31, 2014, respectively.                                                                                                                                                                 

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