| **OTHER ASSETS (As Restated) (Servicing Assets Rollforward) (Details) - Residential MSRs [Member] - USD ($) $ in Thousands** | 3 Months Ended |
|------------------------------------------------------------------------------------------------------------------------------|----------------|
||
| **Servicing Asset at Amortized Value, Balance [Roll Forward]**                                                               |           |   |
| Fair value at beginning of period                                                                                            | $ 145,047      | $ 141,787 |
| Mortgage servicing assets recognized                                                                                         | 3,526          | 1,874 |
| Principal reductions                                                                                                         | (6,131)        | (4,427) |
| Change in fair value due to valuation assumptions                                                                            | (6,990)        | (4,459) |
| Fair value at end of period                                                                                                  | $ 135,452      | $ 134,775 |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of expense charged against earnings for the periodic recognition of servicing assets relative to estimated net servicing income and adjustment made to the carrying value of servicing assets measured using the amortization method related to an other-than-temporary impairment, for example, due to a decrease in future servicing income or an increase in servicing costs.
+ References
No definition available.
+ Details**Name:**sov_ServicingAssetAtAmortizedValueAmortizationAndOtherThanTemporaryImpairments**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**credit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amortized amount of contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=7524895&loc=d3e120260-111741Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122492-111745Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 4 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=56950315&loc=d3e122739-111746
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                     |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of additions from purchases, assumption or transfer to contract to service financial assets under which the benefits of servicing are expected to more than adequately compensate the servicer.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 4 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=56950315&loc=d3e122739-111746
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| X                                                                                                                                                                                                                                                                                                                                              |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.
+ References
No definition available.
+ Details**Name:**us-gaap_ServicingAssetAtAmortizedValueBalanceRollForward**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The net Increase or Decrease in fair value as a result of changes in the inputs, assumptions, or model used to calculate the fair value of servicing assets.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 50 -Section 50 -Paragraph 3 -Subparagraph (a)(4)(i) -URI http://asc.fasb.org/extlink&oid=56950315&loc=d3e122625-111746
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| X                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
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