| **COMMITMENTS, CONTINGENCIES, AND GUARANTEES (Commitments to Extend Credit) (Details) - Commitments to extend credit [Member] - USD ($) $ in Thousands** | Jun. 30, 2015 | Dec. 31, 2014 |
|----------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Commitments [Line Items]**                                                                                                                             |          |          |
| One year or less                                                                                                                                         | $ 5,532,682   | $ 5,968,468   |
| Over 1 year to 3 years                                                                                                                                   | 5,311,031     | 5,322,291     |
| Over 3 years to 5 years                                                                                                                                  | 11,737,849    | 10,810,213    |
| Over 5 years                                                                                                                                             | 6,951,561     | 6,691,090     |
| Total                                                                                                                                                    | $ 29,533,123  | $ 28,792,062  |

| X                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Represents amount committed under commitments.
+ References
No definition available.
+ Details**Name:**sov_CommitmentsAmountCommitted**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Commitments
+ References
No definition available.
+ Details**Name:**sov_CommitmentsLineItems**Namespace Prefix:**sov_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                               |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Represents the amount committed expiring in next twelve months under commitments.
+ References
No definition available.
+ Details**Name:**sov_FairValueDisclosureOffBalanceSheetRisksFaceAmountLiabilityLessThanOneYear**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability, Over Five Years
+ References
No definition available.
+ Details**Name:**sov_FairValueDisclosureOffBalanceSheetRisksFaceAmountLiabilityOverFiveYears**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Represents amount committed expiring in the next two to three years under commitments.
+ References
No definition available.
+ Details**Name:**sov_FairValueDisclosureOffBalanceSheetRisksFaceAmountLiabilityOverOneYearToThreeYears**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                                                                                                                                                                                                                                              |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Fair Value Disclosure, Off-balance Sheet Risks, Face Amount, Liability, Over Three Years to Five Years
+ References
No definition available.
+ Details**Name:**sov_FairValueDisclosureOffBalanceSheetRisksFaceAmountLiabilityOverThreeYearsToFiveYears**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**instant |
| X                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**sov_CommitmentsTypeAxis=us-gaap_CommitmentsToExtendCreditMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |