| **BUSINESS COMBINATIONS (Consolidated Assets Acquired and Liabilities Assumed) (Details) (USD $)** | 0 Months Ended                                                                                                                                                                                                                            |                                 |                                 |
|----------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------|---------------------------------|
||
| **Recognized amounts of identifiable assets acquired and liabilities assumed:**                    |                                                                                                                                                                                                                                      |                            |                            |
| Goodwill                                                                                           |                                                                                                                                                                                                                                      | $ 8,892,011,000us-gaap_Goodwill | $ 8,892,011,000us-gaap_Goodwill |
| SCUSA [Member]                                                                                     |                                                                                                                                                                                                                                      |                            |                            |
| **Business Acquisition [Line Items]**                                                              |                                                                                                                                                                                                                                      |                            |                            |
| Fair value of noncontrolling interest in SCUSA                                                     | 3,273,265,000us-gaap_BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValue/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                                  |                            |                            |
| Fair value of SCUSA employee vested stock options                                                  | 210,181,000sov_BusinessCombinationAcquisitionofEmployeeStockOptionsFairValue/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                                                            |                            |                            |
| Fair value of SHUSA remaining ownership interest in SCUSA                                          | 5,063,881,000sov_BusinessCombinationsAcquisitionofPostIPOOwnershipInterestinAcquiree/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                                                    |                            |                            |
| Fair value of equity-related interests in SCUSA                                                    | 8,547,327,000sov_BusinessCombinationEquityInterestinAcquireeFairValue/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                                                                   |                            |                            |
| **Recognized amounts of identifiable assets acquired and liabilities assumed:**                    |                                                                                                                                                                                                                                      |                            |                            |
| Cash and cash equivalents                                                                          | 11,075,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCashAndEquivalents/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                        |                            |                            |
| Restricted cash                                                                                    | 1,704,906,000sov_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedRestrictedCash/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                             |                            |                            |
| Loan receivables - held for sale                                                                   | 990,137,000sov_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedLoansReceivableHeldforsale/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                   |                            |                            |
| Loan receivables - retail installment contracts                                                    | 19,870,790,000sov_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedLoansReceivableAutos/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                      |                            |                            |
| Loan receivables from dealers                                                                      | 102,689,000sov_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedLoansReceivablefromDealers/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                   |                            |                            |
| Loan receivables - unsecured                                                                       | 1,009,896,000sov_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedLoansReceivableUnsecured/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                   |                            |                            |
| Premises and equipment                                                                             | 74,998,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                 |                            |                            |
| Leased vehicles, net                                                                               | 2,486,929,000sov_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedLoansReceivableLeasedVehicles/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                              |                            |                            |
| Intangibles                                                                                        | 768,750,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                        |                            |                            |
| Miscellaneous receivables and other assets                                                         | 1,061,351,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                  |                            |                            |
| Deferred tax asset                                                                                 | 16,399,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxAssetsNoncurrent/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                               |                            |                            |
| Borrowings and other debt obligations                                                              | (24,497,607,000)us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesLongTermDebt/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                   |                            |                            |
| Accounts payable and accrued liabilities                                                           | (520,568,000)sov_BusinessCombinationRecognizedIdentifiableAssetsAcquiredandLiabilitiesAssumedCurrentLiabilitiesAccountsPayableandAccruedLiabilities/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                     |                            |                            |
| Total identifiable net assets                                                                      | 3,079,745,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNet/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                                    |                            |                            |
| Goodwill                                                                                           | 5,467,582,000us-gaap_Goodwill/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                                                                                                           |                            |                            |
| Stock options awards outstanding, fair value                                                       | 369,300,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                            |                            |                            |
| Stock compensation expense immediately recognized                                                  | 82,600,000us-gaap_AllocatedShareBasedCompensationExpense/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember                                                                                                                                |                            |                            |
| SCUSA [Member] | Executives [Member]                                                               |                                                                                                                                                                                                                                      |                            |                            |
| **Recognized amounts of identifiable assets acquired and liabilities assumed:**                    |                                                                                                                                                                                                                                      |                            |                            |
| Stock options awards outstanding, fair value                                                       | 12,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember/ us-gaap_TitleOfIndividualAxis= sov_ExecutivesMember                        |                            |                            |
| SCUSA [Member] | Stock Compensation Expense [Member]                                               |                                                                                                                                                                                                                                      |                            |                            |
| **Recognized amounts of identifiable assets acquired and liabilities assumed:**                    |                                                                                                                                                                                                                                      |                            |                            |
| Stock options awards outstanding, fair value                                                       | $ 159,100,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingIntrinsicValue/ us-gaap_BusinessAcquisitionAxis= sov_ScusaMember/ us-gaap_IncomeStatementLocationAxis= sov_StockCompensationExpenseMember |                            |                            |

| X                                                                                                                                                                                                                                                                                                                         |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Business Combination, Acquisition of Employee Stock Options, Fair Value
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No definition available.
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| X                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Business Combination, Equity Interest in Acquiree, Fair Value
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No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable and Accrued Liabilities
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Receivable Autos
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No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Receivable from Dealers
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Receivable Held-for-sale
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                     |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Receivable, Leased Vehicles
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                          |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Loans Receivable, Unsecured
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                    |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Restricted Cash
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Business Combinations, Acquisition of Post-IPO Ownership Interest in Acquiree
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                    |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
This element represents the fair value of the noncontrolling interest in the acquiree at the acquisition date.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of currency on hand as well as demand deposits with banks or financial institutions, acquired at the acquisition date. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of deferred tax asset attributable to deductible temporary differences and carryforwards that are expected to be realized or consumed after one year or the normal operating cycle, if longer, acquired at the acquisition date.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of intangible assets, excluding goodwill, acquired at the acquisition date.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount recognized as of the acquisition date for the identifiable assets acquired in excess of (less than) the aggregate liabilities assumed.
+ References
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| - Definition
Amount of long-term debt due after one year or the normal operating cycle, if longer, assumed at the acquisition date.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of other assets expected to be realized or consumed after one year or the normal operating cycle, if longer, acquired at the acquisition date.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of property, plant, and equipment recognized as of the acquisition date.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.
+ References
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.
+ References
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