| **LEASED VEHICLES, NET (Narrative) (Details) - Chrysler Group - USD ($)** | 3 Months Ended | 9 Months Ended  |
|---------------------------------------------------------------------------|----------------|-----------------|
||
| **Operating Leased Assets [Line Items]**                                  |           |            |
| Private label financing agreement, term                                   |           | 10 years        |
| Sale of leases originated, depreciated net capitalized costs              | $ 0            | $ 1,300,000,000 |
| Sale of leases, net book value                                            |           | $ 1,200,000,000 |

| X                                                                                                                                                                                                                                                                                                             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Leases, Sold during the period, Depreciated net capitalized costs
+ References
No definition available.
+ Details**Name:**sov_LeasesSoldduringtheperiodDepreciatednetcapitalizedcosts**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                        |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Leases, Sold during the period, Net book value
+ References
No definition available.
+ Details**Name:**sov_LeasesSoldduringtheperiodNetbookvalue**Namespace Prefix:**sov_**Data Type:**xbrli:monetaryItemType**Balance Type:**debit**Period Type:**duration |
| X                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.
+ References
No definition available.
+ Details**Name:**us-gaap_DebtInstrumentTerm**Namespace Prefix:**us-gaap_**Data Type:**xbrli:durationItemType**Balance Type:**na**Period Type:**duration |
| 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_OperatingLeasedAssetsLineItems**Namespace Prefix:**us-gaap_**Data Type:**xbrli:stringItemType**Balance Type:**na**Period Type:**duration |
| X                                                                                                                                            |
|----------------------------------------------------------------------------------------------------------------------------------------------|
| - Details**Name:**us-gaap_CounterpartyNameAxis=sov_ChryslerGroupMember**Namespace Prefix:****Data Type:**na**Balance Type:****Period Type:** |