| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (As Restated) (Portfolio Segments and Classes) (Details) - USD ($)** | Dec. 31, 2015    | Dec. 31, 2014    |
|--------------------------------------------------------------------------------------------------------------|------------------|------------------|
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Commercial loans                                                                                             | $ 40,712,119,000 | $ 36,641,277,000 |
| Commercial and industrial loans                                                                              |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Commercial loans                                                                                             | 19,874,233,000   | 17,111,922,000   |
| Multifamily loans                                                                                            |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Commercial loans                                                                                             | 9,438,463,000    | 8,705,890,000    |
| Other commercial                                                                                             |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Commercial loans                                                                                             | 2,676,506,000    | 2,084,232,000    |
| Commercial                                                                                                   |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Commercial loans                                                                                             | 40,625,720,000   | 36,622,183,000   |
| Commercial | Corporate banking                                                                               |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Commercial loans                                                                                             | 2,949,089,000    | 3,218,150,000    |
| Commercial | Middle market commercial real estate                                                            |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Commercial loans                                                                                             | 4,223,359,000    | 3,743,099,000    |
| Commercial | Santander real estate capital                                                                   |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Commercial loans                                                                                             | 1,550,469,000    | 1,777,984,000    |
| Commercial | Commercial real estate loans                                                                    |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Commercial loans                                                                                             | 8,722,917,000    | 8,739,233,000    |
| Commercial | Commercial and industrial loans                                                                 |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Commercial loans                                                                                             | 19,787,834,000   | 17,092,828,000   |
| Loans held-for-sale                                                                                          | 86,400,000       | 19,100,000       |
| Commercial | Multifamily loans                                                                               |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Commercial loans                                                                                             | 9,438,463,000    | 8,705,890,000    |
| Commercial | Other commercial                                                                                |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Commercial loans                                                                                             | 2,676,506,000    | 2,084,232,000    |
| Consumer                                                                                                     |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Consumer loans held for investment                                                                           | 38,748,072,000   | 39,373,284,000   |
| Consumer | Residential mortgages                                                                             |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Loans held-for-sale                                                                                          | 236,800,000      | 195,700,000      |
| Consumer | Retail installment contracts                                                                      |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Loans held-for-sale                                                                                          | 900,000,000      | 45,400,000       |
| Consumer | Personal unsecured loans                                                                          |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Loans held-for-sale                                                                                          | 2,000,000,000    | 0                |
| Consumer loans secured by real estate                                                                        |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Consumer loans held for investment                                                                           | 12,382,227,000   | 12,984,873,000   |
| Consumer loans secured by real estate | Residential mortgages                                                |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Consumer loans held for investment                                                                           | 6,230,995,000    | 6,773,575,000    |
| Consumer loans secured by real estate | Home equity loans and lines of credit                                |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Consumer loans held for investment                                                                           | 6,151,232,000    | 6,211,298,000    |
| Consumer loans not secured by real estate | Retail installment contracts and auto loans, originated          |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Consumer loans held for investment                                                                           | 18,539,588,000   | 9,935,503,000    |
| Consumer loans not secured by real estate | Retail installment contracts and auto loans, purchased           |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Consumer loans held for investment                                                                           | 6,108,210,000    | 12,449,526,000   |
| Consumer loans not secured by real estate | Personal unsecured loans                                         |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Consumer loans held for investment                                                                           | 685,467,000      | 2,696,820,000    |
| Consumer loans not secured by real estate | Other consumer                                                   |             |             |
| **Loans Receivable [Line Items]**                                                                            |             |             |
| Consumer loans held for investment                                                                           | $ 1,032,580,000  | $ 1,306,562,000  |

| 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                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Reflects the net carrying amount of commercial loans and leases held in portfolio, after deducting deferred income, but before deducting the allowance for losses on commercial loans and leases.
+ 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=49124121&loc=d3e5074-111524
+ Details**Name:**us-gaap_LoansAndLeasesReceivableCommercialNetOfDeferredIncome**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Reflects the net carrying amount of consumer loans and leases held in portfolio, after deducting deferred income, but before deducting the allowance for losses on consumer loans and leases.
+ 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=49124121&loc=d3e5074-111524
+ Details**Name:**us-gaap_LoansAndLeasesReceivableConsumerNetOfDeferredIncome**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.
+ References
No definition available.
+ Details**Name:**us-gaap_LoansHeldForSaleFairValueDisclosure**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_CommercialAndIndustrialLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_MultiFamilyCommercialLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_OtherCommercialLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_CorporateBankingCommercialLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_MiddleMarketCommercialRealEstateLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_SantanderRealEstateCapitalMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_CommercialRealEstateLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ResidentialMortgageMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_RetailInstallmentContractsMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                     |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_PersonalUnsecuredLoanMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivablePortfolioSegmentAxis=sov_ConsumerLoansSecuredByRealEstateMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivablePortfolioSegmentAxis=sov_ConsumerLoansNotSecuredByRealEstateMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_RetailInstallmentContractsandAutoLoansOriginatedMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_RetailInstallmentContractsandAutoLoansPurchasedMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_OtherConsumerLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |