| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (Consumer Lending Asset Quality Indicators - Credit Score) (Details) - USD ($) $ in Thousands** | Mar. 31, 2019 | Dec. 31, 2018 |
|-----------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Loans Receivable [Line Items]**                                                                                                       |          |          |
| Financing receivable                                                                                                                    | $ 90,416,838  | $ 88,329,146  |
| Consumer | RICs and auto loans                                                                                                          |          |          |
| **Loans Receivable [Line Items]**                                                                                                       |          |          |
| Financing receivable                                                                                                                    | $ 30,456,897  | $ 29,335,220  |
| Percent, RICs and auto loans                                                                                                            | 100.00%       | 100.00%       |
| Consumer | RICs and auto loans | FICO score not applicable                                                                              |          |          |
| **Loans Receivable [Line Items]**                                                                                                       |          |          |
| Financing receivable                                                                                                                    | $ 3,236,902   | $ 3,136,449   |
| Percent, RICs and auto loans                                                                                                            | 10.60%        | 10.70%        |
| Consumer | RICs and auto loans | FICO score less than 600                                                                               |          |          |
| **Loans Receivable [Line Items]**                                                                                                       |          |          |
| Financing receivable                                                                                                                    | $ 15,208,232  | $ 14,884,385  |
| Percent, RICs and auto loans                                                                                                            | 49.90%        | 50.70%        |
| Consumer | RICs and auto loans | FICO score of 600 to 639                                                                               |          |          |
| **Loans Receivable [Line Items]**                                                                                                       |          |          |
| Financing receivable                                                                                                                    | $ 5,414,127   | $ 5,185,412   |
| Percent, RICs and auto loans                                                                                                            | 17.80%        | 17.70%        |
| Consumer | RICs and auto loans | FICO Score of 640 to 679                                                                               |          |          |
| **Loans Receivable [Line Items]**                                                                                                       |          |          |
| Financing receivable                                                                                                                    | $ 4,968,013   | $ 4,758,394   |
| Percent, RICs and auto loans                                                                                                            | 16.30%        | 16.20%        |
| Consumer | RICs and auto loans | FICO Score of 680 to 719                                                                               |          |          |
| **Loans Receivable [Line Items]**                                                                                                       |          |          |
| Financing receivable                                                                                                                    | $ 369,272     | $ 289,270     |
| Percent, RICs and auto loans                                                                                                            | 1.20%         | 1.00%         |
| Consumer | RICs and auto loans | FICO Score of 720 to 759                                                                               |          |          |
| **Loans Receivable [Line Items]**                                                                                                       |          |          |
| Financing receivable                                                                                                                    | $ 356,081     | $ 283,052     |
| Percent, RICs and auto loans                                                                                                            | 1.20%         | 1.00%         |
| Consumer | RICs and auto loans | FICO Score Equal to or Greater than 760                                                                |          |          |
| **Loans Receivable [Line Items]**                                                                                                       |          |          |
| Financing receivable                                                                                                                    | $ 904,270     | $ 798,258     |
| Percent, RICs and auto loans                                                                                                            | 3.00%         | 2.70%         |

| X                                                                                                                                                                                                                                                              |
|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans Receivable, Percentage Of Total Loans
+ References
No definition available.
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| 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.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      |
|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.
+ References
Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.3) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682
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| X                                                                                                                                                   |
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