| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (As Restated) (Retail Installment Contracts and Auto Loans) (Details) - USD ($) $ in Thousands**                                                                                                                                                                                                                                                                                                                                                         | Dec. 31, 2015 | Dec. 31, 2014 |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                |               |          |   |
| Total loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                  | [1],[2]       | $ 79,373,792  | $ 75,995,467 |
| Retail installment contracts and auto loans | Consumer | Consumer loans not secured by real estate                                                                                                                                                                                                                                                                                                                                                                                               |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                |               |          |   |
| Total loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |               | 24,647,798    | 22,385,029 |
| Retail installment contracts, purchased | Consumer | Consumer loans not secured by real estate                                                                                                                                                                                                                                                                                                                                                                                                   |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                |               |          |   |
| UPB                                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |               | 6,709,748     | 13,366,188 |
| UPB - FVO                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |               | 140,995       | 716,923 |
| Total UPB                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |               | 6,850,743     | 14,083,111 |
| Purchase Marks                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |               | (742,533)     | (1,633,585) |
| Total loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |               | 6,108,210     | 12,449,526 |
| Purchase Marks, FVO                                                                                                                                                                                                                                                                                                                                                                                                                                                                              |               | 33,100        | 130,200 |
| Retail installment contracts and auto loans, originated | Consumer | Consumer loans not secured by real estate                                                                                                                                                                                                                                                                                                                                                                                   |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                |               |          |   |
| Total loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |               | 18,539,588    | 9,935,503 |
| Retail installment contracts, originated | Consumer | Consumer loans not secured by real estate                                                                                                                                                                                                                                                                                                                                                                                                  |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                |               |          |   |
| Total UPB                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |               | 19,069,801    | 10,273,931 |
| Total loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |               | 18,521,744    | 9,906,562 |
| Net discount                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |               | (548,057)     | (367,369) |
| Auto Loans | Consumer | Consumer loans not secured by real estate                                                                                                                                                                                                                                                                                                                                                                                                                                |               |          |   |
| **Loans Receivable [Line Items]**                                                                                                                                                                                                                                                                                                                                                                                                                                                                |               |          |   |
| Total loans held for investment                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |               | $ 17,844      | $ 28,941 |
|                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  |
| [1]Loans held for investment includes $328.7 million and $845.9 million of loans recorded at fair value at December 31, 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 8 to these Consolidated Financial Statements for additional information. |

| X                                                                                                                                                                                                                                                                   |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans and Leases Receivable, Net Discounts
+ References
No definition available.
+ Details**Name:**sov_LoansandLeasesReceivableNetDiscounts**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans and Leases Receivable, Purchase Marks
+ References
No definition available.
+ Details**Name:**sov_LoansandLeasesReceivablePurchaseMarks**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans and Leases Receivable, Purchase Marks, Fair Value Option
+ References
No definition available.
+ Details**Name:**sov_LoansandLeasesReceivablePurchaseMarksFairValueOption**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans and Leases Receivable, Unpaid Principal Balance
+ References
No definition available.
+ Details**Name:**sov_LoansandLeasesReceivableUnpaidPrincipalBalance**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans and Leases Receivable, Unpaid Principal Balance, Excluding Fair Value Option
+ References
No definition available.
+ Details**Name:**sov_LoansandLeasesReceivableUnpaidPrincipalBalanceExcludingFairValueOption**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans and Leases Receivable, Unpaid Principal Balance, Fair Value Option
+ References
No definition available.
+ Details**Name:**sov_LoansandLeasesReceivableUnpaidPrincipalBalanceFairValueOption**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**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
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                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_RetailInstallmentContractsandAutoLoansMember**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=sov_ConsumerLoansNotSecuredByRealEstateMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=sov_RetailInstallmentContractsPurchasedMember**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_RetailInstallmentContractsOriginatedMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |
| X                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_FinancialInstrumentAxis=us-gaap_AutomobileLoanMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |