| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (Portfolio Segments and Classes) (Details) (USD $)In Thousands, unless otherwise specified**                                                                                                                                                                                                                                                                                                                                                                    | Mar. 31, 2015                                                                                                                                                                                                                                                                                                                              | Dec. 31, 2014 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | $ 79,882,060us-gaap_NotesReceivableGross                                                                                                                                                                                                                                                                                                   |               | $ 76,292,814us-gaap_NotesReceivableGross |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 78,520,165us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome                                                                                                                                                                                                                                                                              | [1],[2]       | 76,032,562us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome | [1],[2] |
| Commercial and industrial loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 18,859,043us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialAndIndustrialLoansMember                                                                                                                                                                                                                            |               | 17,111,406us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialAndIndustrialLoansMember |  |
| Multi-family loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 8,552,911us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_MultiFamilyCommercialLoansMember                                                                                                                                                                                                                               |               | 8,705,890us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_MultiFamilyCommercialLoansMember |  |
| Other commercial [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 2,148,280us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_OtherCommercialLoansMember                                                                                                                                                                                                                                     |               | 2,084,232us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_OtherCommercialLoansMember |  |
| Residential mortgages [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 7,014,276us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember                                                                                                                                                                                                                                  |               | 6,969,309us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember |  |
| Home equity loans and lines of credit [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 6,171,981us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= us-gaap_HomeEquityMember                                                                                                                                                                                                                                           |               | 6,206,980us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= us-gaap_HomeEquityMember |  |
| Retail installment contracts and auto loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 24,405,668us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember                                                                                                                                                                                                                |               | 22,475,665us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember |  |
| Personal unsecured loan [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 2,696,815us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_PersonalUnsecuredLoanMember                                                                                                                                                                                                                                    |               | 2,696,820us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_PersonalUnsecuredLoanMember |  |
| Corporate banking [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 3,170,416us-gaap_NotesReceivableGross/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_CorporateBankingCommercialLoansMember                                                                                                                                                                            |               | 3,218,151us-gaap_NotesReceivableGross/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_CorporateBankingCommercialLoansMember |  |
| Corporate banking [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 3,170,416us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_CorporateBankingCommercialLoansMember                                                                                                      |               | 3,218,151us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_CorporateBankingCommercialLoansMember |  |
| Middle market commercial real estate [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 3,991,045us-gaap_NotesReceivableGross/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_MiddleMarketCommercialRealEstateLoansMember                                                                                                                                                                      |               | 3,743,100us-gaap_NotesReceivableGross/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_MiddleMarketCommercialRealEstateLoansMember |  |
| Middle market commercial real estate [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 3,991,045us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_MiddleMarketCommercialRealEstateLoansMember                                                                                                |               | 3,743,100us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_MiddleMarketCommercialRealEstateLoansMember |  |
| Santander real estate capital [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 1,638,296us-gaap_NotesReceivableGross/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_SantanderRealEstateCapitalMember                                                                                                                                                                                 |               | 1,777,982us-gaap_NotesReceivableGross/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_SantanderRealEstateCapitalMember |  |
| Santander real estate capital [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 1,638,296us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_SantanderRealEstateCapitalMember                                                                                                           |               | 1,777,982us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_SantanderRealEstateCapitalMember |  |
| Consumer loans secured by real estate [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                          |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 12,888,163us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember                                                                                                                                                   |               | 12,980,555us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember |  |
| Consumer loans secured by real estate [Member] | Residential mortgages [Member]                                                                                                                                                                                                                                                                                                                                                                                                                         |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 6,716,182us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember                                                                                |               | 6,773,575us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember |  |
| Consumer loans secured by real estate [Member] | Home equity loans and lines of credit [Member]                                                                                                                                                                                                                                                                                                                                                                                                         |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 6,171,981us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_HomeEquityMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember                                                                                         |               | 6,206,980us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_HomeEquityMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember |  |
| Consumer loans not secured by real estate [Member] | Retail installment contracts and auto loans [Member]                                                                                                                                                                                                                                                                                                                                                                                               |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 23,386,192us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember                                                           |               | 22,430,241us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember |  |
| Consumer loans not secured by real estate [Member] | Personal unsecured loan [Member]                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 2,696,815us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember                                                                               |               | 2,696,820us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember |  |
| Consumer loans not secured by real estate [Member] | Other consumer [Member]                                                                                                                                                                                                                                                                                                                                                                                                                            |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 1,233,329us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerOtherFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember                                                                |               | 1,303,279us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerOtherFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember |  |
| Commercial Portfolio Segment [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 38,315,666us-gaap_NotesReceivableGross/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember                                                                                                                                                                                                                                         |               | 36,621,667us-gaap_NotesReceivableGross/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Commercial Portfolio Segment [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 8,799,757us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember                                                                                                                                                                    |               | 8,739,233us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Commercial Portfolio Segment [Member] | Commercial and industrial loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                        |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 18,814,718us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialAndIndustrialLoansMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember                                                                                                                                                                |               | 17,092,312us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialAndIndustrialLoansMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Loans held-for-sale                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 44,300us-gaap_LoansHeldForSaleFairValueDisclosure/ us-gaap_FinancialInstrumentAxis= sov_CommercialAndIndustrialLoansMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember                                                                                                                                                     |               | 19,100us-gaap_LoansHeldForSaleFairValueDisclosure/ us-gaap_FinancialInstrumentAxis= sov_CommercialAndIndustrialLoansMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Commercial Portfolio Segment [Member] | Multi-family loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 8,552,911us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_MultiFamilyCommercialLoansMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember                                                                                                                                                                   |               | 8,705,890us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_MultiFamilyCommercialLoansMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Commercial Portfolio Segment [Member] | Other commercial [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 2,148,280us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_OtherCommercialLoansMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember                                                                                                                                                                         |               | 2,084,232us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_OtherCommercialLoansMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Commercial Portfolio Segment [Member] | Corporate banking [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 3,170,416us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_CorporateBankingCommercialLoansMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember                                          |               | 3,218,151us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_CorporateBankingCommercialLoansMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Commercial Portfolio Segment [Member] | Middle market commercial real estate [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                           |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 3,991,045us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_MiddleMarketCommercialRealEstateLoansMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember                                    |               | 3,743,100us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_MiddleMarketCommercialRealEstateLoansMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Commercial Portfolio Segment [Member] | Santander real estate capital [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 1,638,296us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_SantanderRealEstateCapitalMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember                                               |               | 1,777,982us-gaap_NotesReceivableGross/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_SantanderRealEstateCapitalMember/ sov_LoanTypeAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Consumer Portfolio Segment [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 40,204,499us-gaap_NotesReceivableGross/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember                                                                                                                                                                                                                                           |               | 39,410,895us-gaap_NotesReceivableGross/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember |  |
| Consumer Portfolio Segment [Member] | Residential mortgages [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Loans held-for-sale                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 298,100us-gaap_LoansHeldForSaleFairValueDisclosure/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember                                                                                                                                                           |               | 195,700us-gaap_LoansHeldForSaleFairValueDisclosure/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember |  |
| Consumer Portfolio Segment [Member] | Retail installment contracts and auto loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Loans held-for-sale                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     | 1,000,000us-gaap_LoansHeldForSaleFairValueDisclosure/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember                                                                                                                                        |               | 45,400us-gaap_LoansHeldForSaleFairValueDisclosure/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember |  |
| Consumer Portfolio Segment [Member] | Consumer loans secured by real estate [Member]                                                                                                                                                                                                                                                                                                                                                                                                                    |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Financing receivable                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 12,888,163us-gaap_NotesReceivableGross/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember                                                                                                                |               | 12,980,555us-gaap_NotesReceivableGross/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember |  |
| Consumer Portfolio Segment [Member] | Consumer loans secured by real estate [Member] | Residential mortgages [Member]                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 6,716,182us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember                      |               | 6,773,575us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember |  |
| Consumer Portfolio Segment [Member] | Consumer loans secured by real estate [Member] | Home equity loans and lines of credit [Member]                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 6,171,981us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_HomeEquityMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember                               |               | 6,206,980us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_HomeEquityMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember |  |
| Consumer Portfolio Segment [Member] | Consumer loans not secured by real estate [Member] | Retail installment contracts and auto loans [Member]                                                                                                                                                                                                                                                                                                                                                         |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 23,386,192us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember |               | 22,430,241us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember |  |
| Consumer Portfolio Segment [Member] | Consumer loans not secured by real estate [Member] | Personal unsecured loan [Member]                                                                                                                                                                                                                                                                                                                                                                             |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | 2,696,815us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember                     |               | 2,696,820us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember |  |
| Consumer Portfolio Segment [Member] | Consumer loans not secured by real estate [Member] | Other consumer [Member]                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |                                                                                                                                                                                                                                                                                                                                       |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | $ 1,233,329us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerOtherFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember    |               | $ 1,303,279us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerOtherFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember/ sov_LoanTypeAxis= us-gaap_ConsumerPortfolioSegmentMember |  |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
| [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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| - Definition
Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5074-111524Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522
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| - Definition
Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.
+ References
No definition available.
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date. Such amount may include accrued interest receivable in accordance with the terms of the note. The note also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. Excludes amounts related to receivables held-for-sale.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.10(3)) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 10 -Subparagraph 3 -Article 9
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