| **RESTATEMENTS (Additional Information) (Details) - USD ($) $ in Thousands**                                                                            | 3 Months Ended | 6 Months Ended | 12 Months Ended |             |             |
|---------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|-----------------|-------------|-------------|
||
| **Error Corrections and Prior Period Adjustments Restatement [Line Items]**                                                                             |           |           |            |        |        |   |   |   |   |   |   |   |
| Allowance for credit losses                                                                                                                             |           |           | $ 2,834,653     | $ 1,701,602 | $ 1,297,655 | $ 1,090,632 | $ 834,337 | $ 2,834,653 | $ 1,297,655 | $ 1,701,602 | $ 2,281,287 |   |
| Loans held for investment, net                                                                                                                          |           |           | 76,554,535      | 74,293,865  |        |   |   | 76,554,535 |   | 74,293,865 |   |   |
| Interest income - Loans                                                                                                                                 |           |           | 1,936,227       |        | 1,767,980   |   |   | 3,739,905 | 3,096,480 |   |   |   |
| Provision for credit losses                                                                                                                             |           |           | 965,251         |        | 576,357     |   |   | 2,018,890 | 887,226 |   |   |   |
| Miscellaneous income                                                                                                                                    |           |           | 147,490         |        | 200,443     |   |   | 244,030 | 344,582 |   |   |   |
| NET INCOME ATTRIBUTABLE TO SHUSA                                                                                                                        |           |           | 173,024         |        | 261,090     |   |   | 258,440 | 2,027,608 |   |   |   |
| Gain on Change in Control                                                                                                                               |           |           | 0               |        | 0           |   |   | 0 | 2,417,563 |   |   |   |
| Goodwill                                                                                                                                                |           |           | 8,951,484       | 8,951,484   |        |   |   | 8,951,484 |   | 8,951,484 |   | $ 5,530,000 |
| Impairment of long-lived assets                                                                                                                         |           |           | 0               |        | 61,223      | $ 3,300 | $ 33,300 | 0 | 64,546 |   |   |   |
| Overstatement due to Methodology for Estimating the Credit Loss Allowance for Retail Installment Contracts [Member] | Corrections                       |           |           |            |        |        |   |   |   |   |   |   |   |
| **Error Corrections and Prior Period Adjustments Restatement [Line Items]**                                                                             |           |           |            |        |        |   |   |   |   |   |   |   |
| Allowance for credit losses                                                                                                                             |           |           | 208,900         | 358,200     |        |   |   | 208,900 |   | 358,200 |   |   |
| Understatement due to Incorrect Discount Rate Used in the Determination of TDR Impairment [Member] | Corrections                                        |           |           |            |        |        |   |   |   |   |   |   |   |
| **Error Corrections and Prior Period Adjustments Restatement [Line Items]**                                                                             |           |           |            |        |        |   |   |   |   |   |   |   |
| Allowance for credit losses                                                                                                                             |           |           | 41,500          | 1,000       |        |   |   | 41,500 |   | 1,000 |   |   |
| Overstatement (Understatement) due to Incorrect Accretion Methodology [Member] | Corrections                                                            |           |           |            |        |        |   |   |   |   |   |   |   |
| **Error Corrections and Prior Period Adjustments Restatement [Line Items]**                                                                             |           |           |            |        |        |   |   |   |   |   |   |   |
| Allowance for credit losses                                                                                                                             |           |           | 73,400          | 49,200      |        |   |   | 73,400 |   | 49,200 |   |   |
| Loans held for investment, net                                                                                                                          |           |           | 66,525          | 28,647      |        |   |   | 66,525 |   | 28,647 |   |   |
| TDR impairment                                                                                                                                          |           |           | (5,030)         | 817         |        |   |   | (5,030) |   | 817 |   |   |
| Interest income - Loans                                                                                                                                 |           |           | (35,537)        |        | (23,331)    |   |   | (66,418) | (29,351) |   |   |   |
| Provision for credit losses                                                                                                                             |           |           | 26,448          |        | 2,279       |   |   | 32,032 | 2,280 |   |   |   |
| Miscellaneous income                                                                                                                                    |           |           | 2,196           |        | 3,248       |   |   | 5,470 | 4,723 |   |   |   |
| NET INCOME ATTRIBUTABLE TO SHUSA                                                                                                                        |           |           | (6,893)         |        | (17,804)    |   |   | (28,916) | $ (22,348) |   |   |   |
| Corrections at SC that Impacted the Carrying Value of Assets and Liabilities Acquired by SHUSA at the Change in Control [Member] | As Reported          |           |           |            |        |        |   |   |   |   |   |   |   |
| **Error Corrections and Prior Period Adjustments Restatement [Line Items]**                                                                             |           |           |            |        |        |   |   |   |   |   |   |   |
| Gain on Change in Control                                                                                                                               |           |           |            |        |        |   |   |   |   | 2,430,000 |   |   |
| Goodwill                                                                                                                                                |           |           |            |        |        |   |   |   |   |   |   | $ 5,470,000 |
| Correction to Impairment of Indefinite Lived Intangible [Member] | Trade name [Member] | Corrections                                                    |           |           |            |        |        |   |   |   |   |   |   |   |
| **Error Corrections and Prior Period Adjustments Restatement [Line Items]**                                                                             |           |           |            |        |        |   |   |   |   |   |   |   |
| Impairment of intangible assets                                                                                                                         |           |           |            | 28,500      |        |   |   |   |   |   |   |   |
| Correction of Impairment to Capitalized Software [Member] | As Reported                                                                                 |           |           |            |        |        |   |   |   |   |   |   |   |
| **Error Corrections and Prior Period Adjustments Restatement [Line Items]**                                                                             |           |           |            |        |        |   |   |   |   |   |   |   |
| Impairment of long-lived assets                                                                                                                         |           |           |            |        | $ 97,500    |   |   |   |   |   |   |   |
| Retail Installment Contracts [Member] | Overstatement due to Incorrect Discount Rate Used in the Determination of TDR Impairment [Member] | Corrections |           |           |            |        |        |   |   |   |   |   |   |   |
| **Error Corrections and Prior Period Adjustments Restatement [Line Items]**                                                                             |           |           |            |        |        |   |   |   |   |   |   |   |
| Loans held for investment, net                                                                                                                          |           |           | 41,500          | 1,000       |        |   |   | 41,500 |   | 1,000 |   |   |
| Retail Installment Contracts [Member] | Overstatement (Understatement) due to Incorrect Accretion Methodology [Member] | Corrections                    |           |           |            |        |        |   |   |   |   |   |   |   |
| **Error Corrections and Prior Period Adjustments Restatement [Line Items]**                                                                             |           |           |            |        |        |   |   |   |   |   |   |   |
| Loans held for investment, net                                                                                                                          |           |           | $ 26,400        | $ 46,200    |        |   |   | $ 26,400 |   | $ 46,200 |   |   |
| Subsequent Event [Member] | Trade name [Member]                                                                                                         |           |           |            |        |        |   |   |   |   |   |   |   |
| **Error Corrections and Prior Period Adjustments Restatement [Line Items]**                                                                             |           |           |            |        |        |   |   |   |   |   |   |   |
| Impairment of intangible assets                                                                                                                         |           | $ 3,500        |            |        |        |   |   |   |   |   |   |   |
| Subsequent Event [Member] | Correction to Impairment of Indefinite Lived Intangible [Member] | As Reported                                              |           |           |            |        |        |   |   |   |   |   |   |   |
| **Error Corrections and Prior Period Adjustments Restatement [Line Items]**                                                                             |           |           |            |        |        |   |   |   |   |   |   |   |
| Increase in indefinite-lived intangible assets                                                                                                          |           | 50,000         |            |        |        |   |   |   |   |   |   |   |
| Subsequent Event [Member] | Correction to Impairment of Indefinite Lived Intangible [Member] | Trade name [Member] | As Reported                        |           |           |            |        |        |   |   |   |   |   |   |   |
| **Error Corrections and Prior Period Adjustments Restatement [Line Items]**                                                                             |           |           |            |        |        |   |   |   |   |   |   |   |
| Impairment of intangible assets                                                                                                                         | $ 20,300       | $ 11,700       |            |        |        |   |   |   |   |   |   |   |

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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.
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A valuation allowance for financing receivables that are expected to be uncollectible.
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| - Definition
Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.
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| - Definition
Amount of impairment loss resulting from write-down of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit to fair value.
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| - Definition
The aggregate amount of write-downs for impairments recognized during the period for long lived assets held for use (including those held for disposal by means other than sale).
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Amount of increase in assets, excluding financial assets and goodwill, lacking physical substance with an indefinite life, resulting from a business combination.
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| - Definition
The aggregate interest and fee income generated by: (1) loans the Entity has positive intent and ability to hold for the foreseeable future, or until maturity or payoff, including commercial and consumer loans, whether domestic or foreign, which may consist of: (a) industrial and agricultural; (b) real estate; and (c) real estate construction loans; (d) trade financing; (e) lease financing; (f) home equity lines-of-credit; (g) automobile and other vehicle loans; and (h) credit card and other revolving-type loans and (2) loans and leases held-for-sale which may include mortgage loans, direct financing, and sales-type leases.
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| - Definition
Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.
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| - Definition
The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.
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| - Definition
Represents other forms of revenue earned, excluding interest, which is not otherwise specified in the taxonomy.
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| - Definition
Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.
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