| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (Loan and Lease Portfolio Composition) (Details) (USD $)**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                               | Sep. 30, 2014                                                                                                                                                                                                                                                                        | Dec. 31, 2013 |
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| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                 |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | $ 74,526,819,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome                                                                                                                                                                                                                  | [1],[2]       | $ 49,921,677,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome | [1],[2] |
| Loans held for investment with fixed rate of interest                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            | 45,702,579,000us-gaap_LoansReceivableWithFixedRatesOfInterest1                                                                                                                                                                                                                       |               | 23,431,663,000us-gaap_LoansReceivableWithFixedRatesOfInterest1 |  |
| Loans held for investment with variable rate of interest                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         | 28,824,240,000us-gaap_LoansReceivableWithVariableRatesOfInterest1                                                                                                                                                                                                                    |               | 26,490,014,000us-gaap_LoansReceivableWithVariableRatesOfInterest1 |  |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 100.00%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance                                                                                                                                                                                                                      | [2]           | 100.00%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance | [2] |
| Loans held for investment with fixed rate of interest, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    | 61.30%sov_LoansReceivableWithFixedRatesOfInterestPercentageOfTotalLoanBalance                                                                                                                                                                                                        |               | 46.90%sov_LoansReceivableWithFixedRatesOfInterestPercentageOfTotalLoanBalance |  |
| Loans held for investment with variable rate of interest, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 | 38.70%sov_LoansReceivableWithVariableRatesOfInterestPercentageOfTotalLoanBalance                                                                                                                                                                                                     |               | 53.10%sov_LoansReceivableWithVariableRatesOfInterestPercentageOfTotalLoanBalance |  |
| Loans held for investment, deferred income                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       | (1,900,000,000)us-gaap_LoansAndLeasesReceivableDeferredIncome                                                                                                                                                                                                                        |               | 122,600,000us-gaap_LoansAndLeasesReceivableDeferredIncome |  |
| Commercial [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |                                                                                                                                                                                                                                                                                 |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                 |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 35,664,236,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember                                                                                           |               | 32,151,222,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 47.80%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember                                                                                              |               | 64.40%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Commercial [Member] | Commercial real estate loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |                                                                                                                                                                                                                                                                                 |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                 |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 8,685,949,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember                      |               | 9,303,885,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 11.70%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember                        |               | 18.60%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancialInstrumentAxis= sov_CommercialRealEstateLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Commercial [Member] | Commercial and industrial loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                 |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                 |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 16,063,598,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= sov_CommercialAndIndustrialLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember                  |               | 12,820,417,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= sov_CommercialAndIndustrialLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 21.60%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancialInstrumentAxis= sov_CommercialAndIndustrialLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember                     |               | 25.70%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancialInstrumentAxis= sov_CommercialAndIndustrialLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Commercial [Member] | Multi-family loans [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                 |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                 |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 8,941,466,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= sov_MultiFamilyCommercialLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember                     |               | 8,237,029,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= sov_MultiFamilyCommercialLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 12.00%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancialInstrumentAxis= sov_MultiFamilyCommercialLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember                       |               | 16.50%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancialInstrumentAxis= sov_MultiFamilyCommercialLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember |  |
| Commercial [Member] | Other commercial [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                 |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                 |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 1,973,223,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= sov_OtherCommercialLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember                           | [3]           | 1,789,891,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= sov_OtherCommercialLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember | [3] |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 2.50%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancialInstrumentAxis= sov_OtherCommercialLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember                              | [3]           | 3.60%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancialInstrumentAxis= sov_OtherCommercialLoansMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_CommercialPortfolioSegmentMember | [3] |
| Consumer [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                 |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                 |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 38,862,583,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                                                                             |               | 17,770,455,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember |  |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 52.20%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember                                                                                                |               | 35.60%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= us-gaap_ConsumerPortfolioSegmentMember |  |
| Consumer loans secured by real estate [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |                                                                                                                                                                                                                                                                                 |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                 |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 13,574,256,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember                                                                                         |               | 15,872,881,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember |  |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 18.30%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember                                                                                            |               | 31.80%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember |  |
| Consumer loans secured by real estate [Member] | Residential mortgages [Member]                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |                                                                                                                                                                                                                                                                                 |               |   |  |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |                                                                                                                                                                                                                                                                                 |               |   |  |
| Loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 7,358,702,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember                      |               | 9,561,187,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember |  |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 10.00%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancialInstrumentAxis= us-gaap_ResidentialMortgageMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember                        |               | 19.20%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ 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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 6,215,554,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_HomeEquityMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember                               |               | 6,311,694,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_HomeEquityMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember |  |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 8.30%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancialInstrumentAxis= us-gaap_HomeEquityMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansSecuredByRealEstateMember                                  |               | 12.60%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ 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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 21,780,008,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember |               | 81,804,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember |  |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 29.20%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerLoansAutoFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember    |               | 0.20%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ 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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | 2,131,371,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember                     |               | 493,785,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember |  |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 2.90%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancialInstrumentAxis= sov_PersonalUnsecuredLoanMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember                        |               | 1.00%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ 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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        | $ 1,376,948,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerOtherFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember    | [4]           | $ 1,321,985,000us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerOtherFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember | [4] |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                | 1.80%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerOtherFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember         | [4]           | 2.60%sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance/ us-gaap_FinancialInstrumentAxis= us-gaap_ConsumerOtherFinancingReceivableMember/ us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis= sov_ConsumerLoansNotSecuredByRealEstateMember | [4] |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| [1]Loans held for investment includes $1.0 billion and $0.0 billion of loans recorded at fair value at September 30, 2014 and December 31, 2013, respectively.[2]Total loans held for investment includes deferred loan fees, net of deferred origination costs and unamortized purchase premiums, net of discounts as well as purchase accounting adjustments. These items resulted in a net decrease in loan balances of $1.9 billion as of September 30, 2014 and a net increase in loan balances of $122.6 million as of December 31, 2013, respectively. The significant fluctuation between periods is due to the purchase accounting marks resulting from the Change in Control of SCUSA.[3]Other commercial primarily includes commercial equipment vehicle funding ("CEVF") leveraged leases and loans.[4]Other consumer primarily includes recreational vehicles and marine loans. |

| X                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Represents the percentage of total loan balance.
+ References
No definition available.
+ Details**Name:**sov_LoansAndLeasesReceivablePercentageOfTotalLoanBalance**Namespace Prefix:**sov_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans receivable with fixed rates of Interest as a percentage of total loans held for investments portfolio.
+ References
No definition available.
+ Details**Name:**sov_LoansReceivableWithFixedRatesOfInterestPercentageOfTotalLoanBalance**Namespace Prefix:**sov_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
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| - Definition
Loans receivable with variable rates of interest as a percentage of total loans held for investments portfolio.
+ References
No definition available.
+ Details**Name:**sov_LoansReceivableWithVariableRatesOfInterestPercentageOfTotalLoanBalance**Namespace Prefix:**sov_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
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| - Details**Name:**us-gaap_AccountsNotesAndLoansReceivableLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
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| - Definition
Amount of deferred interest and fee income, unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of acquired loans. Excludes amounts for 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 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6378556&loc=d3e10152-111534Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 50 -Paragraph 4 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=25496975&loc=d3e45377-112738Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.7) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Article 9
+ Details**Name:**us-gaap_LoansAndLeasesReceivableDeferredIncome**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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
+ Details**Name:**us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of loan with fixed rate of interest.
+ References
Reference 1: 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
+ Details**Name:**us-gaap_LoansReceivableWithFixedRatesOfInterest1**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of loan with variable or adjustable rate of interest.
+ References
Reference 1: 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
+ Details**Name:**us-gaap_LoansReceivableWithVariableRatesOfInterest1**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_ConsumerLoansNotSecuredByRealEstateMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_ConsumerLoansSecuredByRealEstateMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                              |
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| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |