| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (As Restated) (Loan and Lease Portfolio Composition) (Details) - USD ($) $ in Thousands**                                                                                                                                                                                                                                                                                                                                                                           | Sep. 30, 2015 | Dec. 31, 2014 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| Total commercial loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |               | $ 39,825,473  | $ 36,641,277 |
| Total loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                             | [1],[2]       | 78,583,198    | 75,995,467 |
| Loans held for investment with fixed rate of interest                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               | 46,704,335    | 45,109,343 |
| Loans held for investment with variable rate of interest                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               | $ 31,878,863  | $ 30,886,124 |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               | 100.00%       | 100.00% |
| Loans held for investment with fixed rate of interest, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                               |               | 59.40%        | 59.40% |
| Loans held for investment with variable rate of interest, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                            |               | 40.60%        | 40.60% |
| Net decrease in loan balances                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               | $ 269,900     | $ 1,500,000 |
| Commercial                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| Total commercial loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |               | $ 39,825,473  | $ 36,622,183 |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               | 50.60%        | 48.20% |
| Commercial | Commercial real estate loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| Total commercial loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |               | $ 8,495,182   | $ 8,739,233 |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               | 10.80%        | 11.50% |
| Commercial | Commercial and industrial loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| Total commercial loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |               | $ 19,363,022  | $ 17,092,828 |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               | 24.60%        | 22.50% |
| Commercial | Multi-family loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| Total commercial loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |               | $ 9,600,527   | $ 8,705,890 |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               | 12.20%        | 11.50% |
| Commercial | Other commercial                                                                                                                                                                                                                                                                                                                                                                                                                                                                               |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| Total commercial loans                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |               | $ 2,366,742   | $ 2,084,232 |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               | 3.00%         | 2.70% |
| Consumer                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| Consumer loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |               | $ 38,757,725  | $ 39,373,284 |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               | 49.40%        | 51.80% |
| Consumer loans secured by real estate                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| Consumer loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |               | $ 12,567,700  | $ 12,984,873 |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               | 16.00%        | 17.10% |
| Consumer loans secured by real estate | Residential mortgages                                                                                                                                                                                                                                                                                                                                                                                                                                               |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| Consumer loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |               | $ 6,408,164   | $ 6,773,575 |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               | 8.20%         | 8.90% |
| Consumer loans secured by real estate | Home equity loans and lines of credit                                                                                                                                                                                                                                                                                                                                                                                                                               |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| Consumer loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |               | $ 6,159,536   | $ 6,211,298 |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               | 7.80%         | 8.20% |
| Consumer loans not secured by real estate | Retail installment contracts and auto loans, originated                                                                                                                                                                                                                                                                                                                                                                                                         |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| Consumer loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |               | $ 17,573,943  | $ 9,935,503 |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               | 22.40%        | 13.10% |
| Consumer loans not secured by real estate | Retail installment contracts and auto loans, purchased                                                                                                                                                                                                                                                                                                                                                                                                          |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| Consumer loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |               | $ 6,888,523   | $ 12,449,526 |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               | 8.80%         | 16.40% |
| Consumer loans not secured by real estate | Personal unsecured loans                                                                                                                                                                                                                                                                                                                                                                                                                                        |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| Consumer loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |               | $ 644,548     | $ 2,696,820 |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               | 0.80%         | 3.50% |
| Consumer loans not secured by real estate | Other consumer                                                                                                                                                                                                                                                                                                                                                                                                                                                  |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               |          |   |
| Consumer loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                          |               | $ 1,083,011   | $ 1,306,562 |
| Loans held for investment, percent of total loans                                                                                                                                                                                                                                                                                                                                                                                                                                                           |               | 1.40%         | 1.70% |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
| [1]Loans held for investment includes $374.2 million and $845.9 million of loans recorded at fair value at September 30, 2015 and December 31, 2014, respectively.[2]The Company has interests in certain securitization trusts ("Trusts") that are considered variable interest entities ("VIEs") for accounting purposes. The Company consolidates VIEs where it is deemed the primary beneficiary. See Note 7 to these Condensed Consolidated Financial Statements for additional information. |

| 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 |
| X                                                                                                                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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 |
| 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
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 20 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6378556&loc=d3e10152-111534Reference 2: 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=d3e5074-111524Reference 3: 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 4: 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=d3e45377-112738
+ 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 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522Reference 2: 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_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=us-gaap_CommercialPortfolioSegmentMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_CommercialRealEstateLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_CommercialAndIndustrialLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_MultiFamilyCommercialLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_OtherCommercialLoansMember**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:** |
| X                                                                                                                                                                                                                |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_ConsumerLoansSecuredByRealEstateMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                |
|--------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=us-gaap_HomeEquityMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=sov_ConsumerLoansNotSecuredByRealEstateMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_RetailInstallmentContractsandAutoLoansOriginatedMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_RetailInstallmentContractsandAutoLoansPurchasedMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_PersonalUnsecuredLoanMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_OtherConsumerLoansMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |