| **LEASED VEHICLES, NET (Details) (USD $)**                                                                                                                                                                                                                                                                                      | Mar. 31, 2015                                                                                                                   | Dec. 31, 2014 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------|---------------|
| **Leases [Abstract]**                                                                                                                                                                                                                                                                                                           |                                                                                                                            |               |   |  |
| Leased vehicles                                                                                                                                                                                                                                                                                                                 | $ 9,038,489,000us-gaap_PropertySubjectToOrAvailableForOperatingLeaseGross                                                       |               | $ 8,314,356,000us-gaap_PropertySubjectToOrAvailableForOperatingLeaseGross |  |
| Origination fees and other costs                                                                                                                                                                                                                                                                                                | 25,051,000sov_PropertySubjecttoorAvailableforOperatingLeaseOriginationFeesandOtherCosts                                         |               | 20,628,000sov_PropertySubjecttoorAvailableforOperatingLeaseOriginationFeesandOtherCosts |  |
| Manufacturer subvention payments                                                                                                                                                                                                                                                                                                | (901,348,000)sov_PropertySubjecttoorAvailableforOperatingLeaseManufacturerSubventionPayments                                    |               | (839,150,000)sov_PropertySubjecttoorAvailableforOperatingLeaseManufacturerSubventionPayments |  |
| Total leased vehicles                                                                                                                                                                                                                                                                                                           | 8,162,192,000sov_PropertySubjecttoorAvailableforOperatingLeaseGrossIncludingInitialDirectCostsandManufacturerSubventionPayments |               | 7,495,834,000sov_PropertySubjecttoorAvailableforOperatingLeaseGrossIncludingInitialDirectCostsandManufacturerSubventionPayments |  |
| Less: accumulated depreciation                                                                                                                                                                                                                                                                                                  | (1,088,437,000)us-gaap_PropertySubjectToOrAvailableForOperatingLeaseAccumulatedDepreciation                                     |               | (857,719,000)us-gaap_PropertySubjectToOrAvailableForOperatingLeaseAccumulatedDepreciation |  |
| Leased vehicles, net                                                                                                                                                                                                                                                                                                            | 7,073,755,000us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNet                                                           | [1]           | 6,638,115,000us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNet | [1] |
| Chrysler Capital leases, depreciated net capitalized cost                                                                                                                                                                                                                                                                       | 561,300,000sov_CapitalLeasedAssetsDepreciableValue                                                                              |               |   |  |
| Chrysler Capital leases, net book value                                                                                                                                                                                                                                                                                         | $ 488,900,000us-gaap_CapitalLeasesBalanceSheetAssetsByMajorClassNet                                                             |               |   |  |
|                                                                                                                                                                                                                                                                                                                                 |
| [1]The Company has interests in certain securitization trusts ("Trusts") that are considered variable interest entities ("VIEs") for accounting purposes. The Company consolidates VIEs where it is deemed the primary beneficiary. See Note 7 to these Condensed Consolidated Financial Statements for additional information. |

| X                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Capital Leased Assets, Depreciable Value
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No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                  |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Property Subject to or Available for Operating Lease, Gross, Including Initial Direct Costs and Manufacturer Subvention Payments
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                      |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Property Subject to or Available for Operating Lease, Origination Fees and Other Costs
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The total gross amount less the charge for the use of the long-lived depreciable assets subject to a lease meeting the criteria for capitalization.
+ References
Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6455398&loc=d3e45280-112737
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                        |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of accumulated depreciation, by major property class, recorded on property subject to or available for lease as of the balance sheet date.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 |
|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount before accumulated depreciation of physical assets used in the normal conduct of business to produce goods and services subject to or available for lease.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The amount of property, by major property class, net of accumulated depreciation, subject to or available for lease as of the balance sheet date.
+ References
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