| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (As Restated) (Consumer Lending Asset Quality Indicators-CLTV Range) (Details) - USD ($) $ in Thousands** | Mar. 31, 2015 | Dec. 31, 2014 | Mar. 31, 2014 |
|---------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|---------------|
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 79,800,855  |          | $ 74,317,576  |
| Home mortgages [Member]                                                                                                                           |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 7,014,276   | $ 6,969,309   |          |
| Percentage of total home mortgages                                                                                                                | 100.00%       | 100.00%       |          |
| Self-originated home equity [Member]                                                                                                              |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 6,176,299   | $ 6,211,298   |          |
| Percentage of total self-originated home equity loans                                                                                             | 100.00%       | 100.00%       |          |
| LTV of less than or equal to 80% [Member] | Home mortgages [Member]                                                                               |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 5,651,633   | $ 5,732,061   |          |
| Percentage of total home mortgages                                                                                                                | 80.60%        | 82.20%        |          |
| LTV of less than or equal to 80% [Member] | Self-originated home equity [Member]                                                                  |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 4,744,219   | $ 4,951,656   |          |
| Percentage of total self-originated home equity loans                                                                                             | 76.80%        | 79.70%        |          |
| LTV of 80.01% to 90% [Member] | Home mortgages [Member]                                                                                           |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 426,877     | $ 396,356     |          |
| Percentage of total home mortgages                                                                                                                | 6.10%         | 5.70%         |          |
| LTV of 80.01% to 90% [Member] | Self-originated home equity [Member]                                                                              |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 495,560     | $ 386,096     |          |
| Percentage of total self-originated home equity loans                                                                                             | 8.00%         | 6.20%         |          |
| LTV of 90.01% to 100% [Member] | Home mortgages [Member]                                                                                          |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 252,790     | $ 215,803     |          |
| Percentage of total home mortgages                                                                                                                | 3.60%         | 3.10%         |          |
| LTV of 90.01% to 100% [Member] | Self-originated home equity [Member]                                                                             |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 232,123     | $ 199,850     |          |
| Percentage of total self-originated home equity loans                                                                                             | 3.80%         | 3.20%         |          |
| LTV of 100.01% to 120% [Member] | Home mortgages [Member]                                                                                         |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 142,295     | $ 143,925     |          |
| Percentage of total home mortgages                                                                                                                | 2.00%         | 2.10%         |          |
| LTV of 100.01% to 120% [Member] | Self-originated home equity [Member]                                                                            |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 242,189     | $ 215,483     |          |
| Percentage of total self-originated home equity loans                                                                                             | 3.90%         | 3.50%         |          |
| LTV of 120.01% to 140% [Member] | Home mortgages [Member]                                                                                         |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 48,189      | $ 57,949      |          |
| Percentage of total home mortgages                                                                                                                | 0.70%         | 0.80%         |          |
| LTV of 120.01% to 140% [Member] | Self-originated home equity [Member]                                                                            |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 82,148      | $ 70,438      |          |
| Percentage of total self-originated home equity loans                                                                                             | 1.30%         | 1.10%         |          |
| LTV greater than 140% [Member] | Home mortgages [Member]                                                                                          |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 44,339      | $ 54,446      |          |
| Percentage of total home mortgages                                                                                                                | 0.60%         | 0.80%         |          |
| LTV greater than 140% [Member] | Self-originated home equity [Member]                                                                             |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 73,136      | $ 63,468      |          |
| Percentage of total self-originated home equity loans                                                                                             | 1.20%         | 1.00%         |          |
| LTV not applicable [Member] | Home mortgages [Member]                                                                                             |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 448,153     | $ 368,769     |          |
| Percentage of total home mortgages                                                                                                                | 6.40%         | 5.30%         |          |
| LTV not applicable [Member] | Self-originated home equity [Member]                                                                                |          |          |          |
| **Loans Receivable [Line Items]**                                                                                                                 |          |          |          |
| Financing receivable                                                                                                                              | $ 306,924     | $ 324,307     |          |
| Percentage of total self-originated home equity loans                                                                                             | 5.00%         | 5.30%         |          |

| X                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The balance of financing receivables including loans held-for-sale, before allowance for credit losses.
+ References
No definition available.
+ Details**Name:**sov_FinancingReceivableIncludingReceivableHeldForSaleGross**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans and Leases Receivable, Percentage of Total Loans, Home Mortgages
+ References
No definition available.
+ Details**Name:**sov_LoansAndLeasesReceivablePercentageOfTotalLoansHomeMortgages**Namespace Prefix:**sov_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans and Leases Receivable, Percentage of Total Loans, Self-originated Home Equity
+ References
No definition available.
+ Details**Name:**sov_LoansAndLeasesReceivablePercentageOfTotalLoansSelfOriginatedHomeEquity**Namespace Prefix:**sov_**Data Type:**num:percentItemType**Balance Type:**na**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.
+ References
No definition available.
+ Details**Name:**us-gaap_AccountsNotesAndLoansReceivableLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                             |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_HomeMortgagesMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_SelfOriginatedHomeEquityMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=sov_LtvOfLessThanOrEqualTo80Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=sov_LtvOf8001To90Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=sov_LtvOf9001To100Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=sov_LtvOf10001To120Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=sov_LtvOf12001To140Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=sov_LtvGreaterThan140Member**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_InternalCreditAssessmentAxis=sov_LtvNotApplicableMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |