| **FAIR VALUE (Fair Value Measurements, Non-recurring) (Details) - USD ($) $ in Thousands**       | Jun. 30, 2020 | Dec. 31, 2019 |
|--------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired loans                                                                                   | $ 72,900      | $ 102,000     |
| LHFS                                                                                             | 241,300       | 289,000       |
| Nonrecurring                                                                                     |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Foreclosed assets                                                                                | 49,358        | 68,248        |
| Vehicle inventory                                                                                | 294,156       | 346,265       |
| LHFS                                                                                             | 5,198,114     | 1,131,214     |
| MSRs                                                                                             | 7,318         | 8,197         |
| Nonrecurring | Lower-of-cost-or fair value                                                       |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| LHFS                                                                                             | 2,600,000     |          |
| Nonrecurring | Impaired commercial LHFI                                                          |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired loans                                                                                   | 185,261       | 489,860       |
| Total carrying value of the loans                                                                | 175,800       | 448,800       |
| Nonrecurring | Auto loans impaired due to bankruptcy                                             |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired loans                                                                                   | 187,837       | 201,007       |
| Goodwill                                                                                         | 350,000       | 0             |
| Nonrecurring | Impaired personal loans held for sale                                             |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| LHFS                                                                                             | 808,400       | 1,000,000     |
| 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             |
| MSRs                                                                                             | 0             | 0             |
| Nonrecurring | Level 1 | Impaired commercial LHFI                                                |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired loans                                                                                   | 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 loans                                                                                   | 0             | 0             |
| Goodwill                                                                                         | 0             | 0             |
| Nonrecurring | Level 2                                                                           |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Foreclosed assets                                                                                | 8,693         | 17,168        |
| Vehicle inventory                                                                                | 294,156       | 346,265       |
| LHFS                                                                                             | 103           | 0             |
| MSRs                                                                                             | 0             | 0             |
| Nonrecurring | Level 2 | Impaired commercial LHFI                                                |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired loans                                                                                   | 52,195        | 133,640       |
| Nonrecurring | Level 2 | Auto loans impaired due to bankruptcy                                   |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired loans                                                                                   | 187,837       | 200,504       |
| Goodwill                                                                                         | 0             | 0             |
| Nonrecurring | Level 3                                                                           |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Foreclosed assets                                                                                | 40,665        | 51,080        |
| Vehicle inventory                                                                                | 0             | 0             |
| LHFS                                                                                             | 5,198,011     | 1,131,214     |
| MSRs                                                                                             | 7,318         | 8,197         |
| Nonrecurring | Level 3 | Impaired commercial LHFI                                                |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired loans                                                                                   | 133,066       | 356,220       |
| Nonrecurring | Level 3 | Auto loans impaired due to bankruptcy                                   |          |          |
| **Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]** |          |          |
| Impaired loans                                                                                   | 0             | 503           |
| Goodwill                                                                                         | $ 350,000     | $ 0           |

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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.
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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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Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.
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