| **FAIR VALUE - Fair Value Measurements, Non-recurring (Details) - USD ($)**                      | Sep. 30, 2023 | Dec. 31, 2022 |
|--------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired commercial LHFI                                                                         | $ 15,400,000  | $ 20,900,000  |
| LHFS                                                                                             | 488,000       | 549,000       |
| Nonrecurring                                                                                     |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Foreclosed assets                                                                                | 38,640,000    | 4,108,000     |
| Vehicle inventory                                                                                | 299,115,000   | 246,970,000   |
| LHFS                                                                                             | 435,321,000   | 99,006,000    |
| Goodwill                                                                                         | 2,766,665,000 | 2,767,732,000 |
| Nonrecurring | Impaired commercial LHFI                                                          |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired commercial LHFI                                                                         | 167,044,000   | 84,927,000    |
| Nonrecurring | Auto loans impaired due to bankruptcy                                             |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired commercial LHFI                                                                         | 167,106,000   | 212,866,000   |
| Nonrecurring | Level 1                                                                           |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Foreclosed assets                                                                                | 0             | 0             |
| Vehicle inventory                                                                                | 0             | 0             |
| LHFS                                                                                             | 0             | 0             |
| Goodwill                                                                                         | 0             | 0             |
| Nonrecurring | Level 1 | Impaired commercial LHFI                                                |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired commercial LHFI                                                                         | 0             | 0             |
| Nonrecurring | Level 1 | Auto loans impaired due to bankruptcy                                   |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired commercial LHFI                                                                         | 0             | 0             |
| Nonrecurring | Level 2                                                                           |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Foreclosed assets                                                                                | 38,640,000    | 4,108,000     |
| Vehicle inventory                                                                                | 299,115,000   | 246,970,000   |
| LHFS                                                                                             | 0             | 0             |
| Goodwill                                                                                         | 0             | 0             |
| Nonrecurring | Level 2 | Impaired commercial LHFI                                                |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired commercial LHFI                                                                         | 56,170,000    | 33,133,000    |
| Nonrecurring | Level 2 | Auto loans impaired due to bankruptcy                                   |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired commercial LHFI                                                                         | 167,106,000   | 212,866,000   |
| Nonrecurring | Level 3                                                                           |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Foreclosed assets                                                                                | 0             | 0             |
| Vehicle inventory                                                                                | 0             | 0             |
| LHFS                                                                                             | 435,321,000   | 99,006,000    |
| Goodwill                                                                                         | 2,766,665,000 | 2,767,732,000 |
| Nonrecurring | Level 3 | Impaired commercial LHFI                                                |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired commercial LHFI                                                                         | 110,874,000   | 51,794,000    |
| Nonrecurring | Level 3 | Auto loans impaired due to bankruptcy                                   |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired commercial LHFI                                                                         | $ 0           | $ 0           |

| X                                                                                                                                                                                                                                                               |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Foreclosed Assets Measured at Fair Value
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| - 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.
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| - Definition
Fair value portion of asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.
+ References
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| X                                                                                                                                                                                                                                                                                                                                               |
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| - Definition
Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.
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| - Definition
Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.
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