| **VARIABLE INTEREST ENTITIES (As Restated) (Assets and Liabilities of VIEs) (Details) - USD ($) $ in Thousands** | Mar. 31, 2015 | Dec. 31, 2014 |
|------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Variable Interest Entity and Securitizations [Abstract]**                                                      |          |          |
| Restricted cash                                                                                                  | $ 1,852,825   | $ 1,626,257   |
| RICs, net                                                                                                        | 22,277,343    | 20,557,168    |
| RIC's held-for-sale                                                                                              | 1,100,000     | 18,700        |
| Leased vehicles, net                                                                                             | 5,025,109     | 4,848,593     |
| Various other assets                                                                                             | 533,714       | 555,108       |
| Total Assets                                                                                                     | 29,688,991    | 27,587,126    |
| Notes payable                                                                                                    | 29,782,279    | 27,892,669    |
| Various other liabilities                                                                                        | 63,249        | 55,795        |
| Total Liabilities                                                                                                | $ 29,845,528  | $ 27,948,464  |

| X                                                                                                                                                                                                                                                                                                                       |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Variable Interest Entity, Consolidated, Carrying Amount, Notes Payable
+ References
No definition available.
+ Details**Name:**sov_VariableInterestEntityConsolidatedCarryingAmountNotesPayable**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                    |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Variable Interest Entity, Consolidated, Carrying Amount, Other Assets
+ References
No definition available.
+ Details**Name:**sov_VariableInterestEntityConsolidatedCarryingAmountOtherAssets**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                               |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Variable Interest Entity, Consolidated, Carrying Amount, Other Liabilities
+ References
No definition available.
+ Details**Name:**sov_VariableInterestEntityConsolidatedCarryingAmountOtherLiabilities**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Variable Interest Entity, Consolidated, Carrying Amount, Property Subject to or Available for Operating Lease, Net
+ References
No definition available.
+ Details**Name:**sov_VariableInterestEntityConsolidatedCarryingAmountPropertySubjecttoorAvailableforOperatingLeaseNet**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                          |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Variable Interest Entity, Consolidated, Carrying Amount, Restricted Cash
+ References
No definition available.
+ Details**Name:**sov_VariableInterestEntityConsolidatedCarryingAmountRestrictedCash**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Variable Interest Entity, Consolidated, Carrying Amount, Retail Installment Contracts, Held-for-Sale, Net
+ References
No definition available.
+ Details**Name:**sov_VariableInterestEntityConsolidatedCarryingAmountRetailInstallmentContractsHeldforSaleNet**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Variable Interest Entity, Consolidated, Carrying Amount, Retail Installment Contracts, Net
+ References
No definition available.
+ Details**Name:**sov_VariableInterestEntityConsolidatedCarryingAmountRetailInstallmentContractsNet**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                       |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Variable Interest Entity and Securitizations [Abstract]
+ References
No definition available.
+ Details**Name:**sov_VariableInterestEntityandSecuritizationsAbstract**Namespace Prefix:**sov_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The carrying amount of the consolidated Variable Interest Entity's assets included in the reporting entity's statement of financial position.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=52262685&loc=d3e5710-111685
+ Details**Name:**us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssets**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The carrying amount of the consolidated Variable Interest Entity's liabilities included in the reporting entity's statement of financial position.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (bb) -URI http://asc.fasb.org/extlink&oid=52262685&loc=d3e5710-111685
+ Details**Name:**us-gaap_VariableInterestEntityConsolidatedCarryingAmountLiabilities**Namespace Prefix:**us-gaap_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |