| **LOANS AND ALLOWANCE FOR CREDIT LOSSES (Rollforward of Allowance for Credit Losses) (Details) - USD ($) $ in Thousands** | 3 Months Ended | 6 Months Ended |
|---------------------------------------------------------------------------------------------------------------------------|----------------|----------------|
||
| **Allowance for Loan Losses [Roll Forward]**                                                                              |           |           |   |   |   |
| Allowance for loan and lease losses, beginning of period                                                                  | $ 3,480,603    | $ 2,281,287    | $ 1,701,602 | $ 3,160,711 | $ 1,701,602 |
| Provision for loan and lease losses                                                                                       | 613,943        | 955,251        |   | 1,471,611 | 2,013,890 |
| Other                                                                                                                     |           |           |   |   | (27,117) |
| Charge-offs                                                                                                               | (1,052,192)    | (911,148)      |   | (2,221,922) | (1,873,462) |
| Recoveries                                                                                                                | 632,914        | 509,263        |   | 1,264,868 | 1,019,740 |
| Charge-offs, net of recoveries                                                                                            | (419,278)      | (401,885)      |   | (957,054) | (853,722) |
| Allowance for loan and lease losses, end of period                                                                        | 3,675,268      | 2,834,653      | 2,281,287 | 3,675,268 | 2,834,653 |
| Reserve for unfunded lending commitments, beginning of period                                                             | 172,008        | 127,641        | 132,641 | 147,396 | 132,641 |
| Provision for unfunded lending commitments                                                                                | (16,634)       | 10,000         |   | 7,977 | 5,000 |
| Loss on unfunded lending commitments                                                                                      | (166)          | 0              |   | (165) | 0 |
| Reserve for unfunded lending commitments, end of period                                                                   | 155,208        | 137,641        | 127,641 | 155,208 | 137,641 |
| Total allowance for credit losses, end of period                                                                          | 3,830,476      | 2,972,294      |   | 3,830,476 | 2,972,294 |
| Ending balance, individually evaluated for impairment                                                                     | 1,355,832      | 654,739        |   | 1,355,832 | 654,739 |
| Ending balance, collectively evaluated for impairment                                                                     | 2,319,436      | 2,179,914      |   | 2,319,436 | 2,179,914 |
| **Financing receivables:**                                                                                                |           |           |   |   |   |
| Ending balance                                                                                                            | 83,827,934     | 81,275,278     |   | 83,827,934 | 81,275,278 |
| Ending balance, evaluated under the fair value option or lower of cost or fair value(2)                                   | 3,507,861      | 2,380,741      |   | 3,507,861 | 2,380,741 |
| Ending balance, individually evaluated for impairment                                                                     | 5,443,573      | 4,187,666      |   | 5,443,573 | 4,187,666 |
| Ending balance, collectively evaluated for impairment                                                                     | 74,876,500     | 74,706,871     |   | 74,876,500 | 74,706,871 |
| Sale of TDRs and NPLs classified as held-for-sale                                                                         |           |           | 1,000,000 |   |   |
| Commercial                                                                                                                |           |           |   |   |   |
| **Allowance for Loan Losses [Roll Forward]**                                                                              |           |           |   |   |   |
| Allowance for loan and lease losses, beginning of period                                                                  | 531,850        | 413,014        | 401,553 | 435,717 | 401,553 |
| Provision for loan and lease losses                                                                                       | (20,841)       | 13,353         |   | 90,193 | 38,153 |
| Other                                                                                                                     |           |           |   |   | 0 |
| Charge-offs                                                                                                               | (32,533)       | (31,846)       |   | (72,849) | (51,184) |
| Recoveries                                                                                                                | 21,223         | 8,174          |   | 46,638 | 14,173 |
| Charge-offs, net of recoveries                                                                                            | (11,310)       | (23,672)       |   | (26,211) | (37,011) |
| Allowance for loan and lease losses, end of period                                                                        | 499,699        | 402,695        | 413,014 | 499,699 | 402,695 |
| Reserve for unfunded lending commitments, beginning of period                                                             | 172,008        | 127,641        | 132,641 | 147,396 | 132,641 |
| Provision for unfunded lending commitments                                                                                | (16,634)       | 10,000         |   | 7,977 | 5,000 |
| Loss on unfunded lending commitments                                                                                      | (166)          | 0              |   | (165) | 0 |
| Reserve for unfunded lending commitments, end of period                                                                   | 155,208        | 137,641        | 127,641 | 155,208 | 137,641 |
| Total allowance for credit losses, end of period                                                                          | 654,907        | 540,336        |   | 654,907 | 540,336 |
| Ending balance, individually evaluated for impairment                                                                     | 129,084        | 60,139         |   | 129,084 | 60,139 |
| Ending balance, collectively evaluated for impairment                                                                     | 370,615        | 342,556        |   | 370,615 | 342,556 |
| **Financing receivables:**                                                                                                |           |           |   |   |   |
| Ending balance                                                                                                            | 41,564,581     | 39,001,911     |   | 41,564,581 | 39,001,911 |
| Ending balance, evaluated under the fair value option or lower of cost or fair value(2)                                   | 464,265        | 1,012          |   | 464,265 | 1,012 |
| Ending balance, individually evaluated for impairment                                                                     | 628,642        | 407,208        |   | 628,642 | 407,208 |
| Ending balance, collectively evaluated for impairment                                                                     | 40,471,674     | 38,593,691     |   | 40,471,674 | 38,593,691 |
| Consumer                                                                                                                  |           |           |   |   |   |
| **Allowance for Loan Losses [Roll Forward]**                                                                              |           |           |   |   |   |
| Allowance for loan and lease losses, beginning of period                                                                  | 2,903,425      | 1,796,974      | 1,267,025 | 2,679,666 | 1,267,025 |
| Provision for loan and lease losses                                                                                       | 634,784        | 941,605        |   | 1,381,418 | 1,937,169 |
| Other                                                                                                                     |           |           |   |   | (27,117) |
| Charge-offs                                                                                                               | (1,019,659)    | (879,302)      |   | (2,149,073) | (1,822,278) |
| Recoveries                                                                                                                | 611,691        | 501,089        |   | 1,218,230 | 1,005,567 |
| Charge-offs, net of recoveries                                                                                            | (407,968)      | (378,213)      |   | (930,843) | (816,711) |
| Allowance for loan and lease losses, end of period                                                                        | 3,130,241      | 2,360,366      | 1,796,974 | 3,130,241 | 2,360,366 |
| Reserve for unfunded lending commitments, beginning of period                                                             | 0              | 0              | 0 | 0 | 0 |
| Provision for unfunded lending commitments                                                                                | 0              | 0              |   | 0 | 0 |
| Loss on unfunded lending commitments                                                                                      | 0              | 0              |   | 0 | 0 |
| Reserve for unfunded lending commitments, end of period                                                                   | 0              | 0              | 0 | 0 | 0 |
| Total allowance for credit losses, end of period                                                                          | 3,130,241      | 2,360,366      |   | 3,130,241 | 2,360,366 |
| Ending balance, individually evaluated for impairment                                                                     | 1,226,748      | 594,600        |   | 1,226,748 | 594,600 |
| Ending balance, collectively evaluated for impairment                                                                     | 1,903,493      | 1,765,766      |   | 1,903,493 | 1,765,766 |
| **Financing receivables:**                                                                                                |           |           |   |   |   |
| Ending balance                                                                                                            | 42,263,353     | 42,273,367     |   | 42,263,353 | 42,273,367 |
| Ending balance, evaluated under the fair value option or lower of cost or fair value(2)                                   | 3,043,596      | 2,379,729      |   | 3,043,596 | 2,379,729 |
| Ending balance, individually evaluated for impairment                                                                     | 4,814,931      | 3,780,458      |   | 4,814,931 | 3,780,458 |
| Ending balance, collectively evaluated for impairment                                                                     | 34,404,826     | 36,113,180     |   | 34,404,826 | 36,113,180 |
| Unallocated                                                                                                               |           |           |   |   |   |
| **Allowance for Loan Losses [Roll Forward]**                                                                              |           |           |   |   |   |
| Allowance for loan and lease losses, beginning of period                                                                  | 45,328         | 71,299         | 33,024 | 45,328 | 33,024 |
| Provision for loan and lease losses                                                                                       | 0              | 293            |   | 0 | 38,568 |
| Other                                                                                                                     |           |           |   |   | 0 |
| Charge-offs                                                                                                               | 0              | 0              |   | 0 | 0 |
| Recoveries                                                                                                                | 0              | 0              |   | 0 | 0 |
| Charge-offs, net of recoveries                                                                                            | 0              | 0              |   | 0 | 0 |
| Allowance for loan and lease losses, end of period                                                                        | 45,328         | 71,592         | 71,299 | 45,328 | 71,592 |
| Reserve for unfunded lending commitments, beginning of period                                                             | 0              | 0              | 0 | 0 | 0 |
| Provision for unfunded lending commitments                                                                                | 0              | 0              |   | 0 | 0 |
| Loss on unfunded lending commitments                                                                                      | 0              | 0              |   | 0 | 0 |
| Reserve for unfunded lending commitments, end of period                                                                   | 0              | 0              | 0 | 0 | 0 |
| Total allowance for credit losses, end of period                                                                          | 45,328         | 71,592         |   | 45,328 | 71,592 |
| Ending balance, individually evaluated for impairment                                                                     | 0              | 0              |   | 0 | 0 |
| Ending balance, collectively evaluated for impairment                                                                     | 45,328         | 71,592         |   | 45,328 | 71,592 |
| **Financing receivables:**                                                                                                |           |           |   |   |   |
| Ending balance                                                                                                            | 0              | 0              |   | 0 | 0 |
| Ending balance, evaluated under the fair value option or lower of cost or fair value(2)                                   | 0              | 0              |   | 0 | 0 |
| Ending balance, individually evaluated for impairment                                                                     | 0              | 0              |   | 0 | 0 |
| Ending balance, collectively evaluated for impairment                                                                     | 0              | 0              |   | 0 | 0 |
| Retail installment contracts and auto loans - purchased | Consumer                                                        |           |           |   |   |   |
| **Allowance for Loan Losses [Roll Forward]**                                                                              |           |           |   |   |   |
| Allowance for loan and lease losses, beginning of period                                                                  | 589,107        | 319,231        | 963 | 590,807 | 963 |
| Provision for loan and lease losses                                                                                       | 47,617         | 330,724        |   | 121,252 | 829,629 |
| Other                                                                                                                     | 0              | 0              |   | 0 | (27,117) |
| Charge-offs                                                                                                               | (194,169)      | (399,788)      |   | (458,961) | (887,412) |
| Recoveries                                                                                                                | 173,068        | 292,542        |   | 362,525 | 626,646 |
| Charge-offs, net of recoveries                                                                                            | (21,101)       | (107,246)      |   | (96,436) | (260,766) |
| Allowance for loan and lease losses, end of period                                                                        | 615,623        | 542,709        | 319,231 | 615,623 | 542,709 |
| Retail installment contracts and auto loans - originated | Consumer                                                       |           |           |   |   |   |
| **Allowance for Loan Losses [Roll Forward]**                                                                              |           |           |   |   |   |
| Allowance for loan and lease losses, beginning of period                                                                  | 2,137,270      | 920,153        | 709,024 | 1,891,989 | 709,024 |
| Provision for loan and lease losses                                                                                       | 572,145        | 454,219        |   | 1,246,565 | 834,357 |
| Other                                                                                                                     | 0              | 0              |   | 0 | 0 |
| Charge-offs                                                                                                               | (789,788)      | (337,204)      |   | (1,614,868) | (656,206) |
| Recoveries                                                                                                                | 422,813        | 181,966        |   | 818,754 | 331,959 |
| Charge-offs, net of recoveries                                                                                            | (366,975)      | (155,238)      |   | (796,114) | (324,247) |
| Allowance for loan and lease losses, end of period                                                                        | 2,342,440      | 1,219,134      | 920,153 | 2,342,440 | 1,219,134 |
| Retail installment contracts and auto loans - originated | Consumer                                                       |           |           |   |   |   |
| **Allowance for Loan Losses [Roll Forward]**                                                                              |           |           |   |   |   |
| Allowance for loan and lease losses, beginning of period                                                                  | 2,726,377      | 1,239,384      | 709,987 | 2,482,796 | 709,987 |
| Provision for loan and lease losses                                                                                       | 619,762        | 784,943        |   | 1,367,817 | 1,663,986 |
| Other                                                                                                                     | 0              | 0              |   | 0 | (27,117) |
| Charge-offs                                                                                                               | (983,957)      | (736,992)      |   | (2,073,829) | (1,543,618) |
| Recoveries                                                                                                                | 595,881        | 474,508        |   | 1,181,279 | 958,605 |
| Charge-offs, net of recoveries                                                                                            | (388,076)      | (262,484)      |   | (892,550) | (585,013) |
| Allowance for loan and lease losses, end of period                                                                        | $ 2,958,063    | $ 1,761,843    | $ 1,239,384 | $ 2,958,063 | $ 1,761,843 |

| X                                                                                                                                                                                                                                                                                                                                                                                                   |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
A valuation allowance for financing receivables that are expected to be uncollectible and reserve for unfunded lending commitments.
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No definition available.
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Net amount of direct write-downs and recoveries of financing receivables charged against the allowance.
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No definition available.
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Gain (Loss) on Unfunded Commitments
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| - Definition
Increase (Decrease) in Allowance for Credit Losses from Sale of Troubled Debt Restructuring and Non-performing Loans Held-for-sale
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No definition available.
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Loans Receivable Held-for-sale, Net, Fair Value Option
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| - Definition
Net change in reserve for unfunded commitments which is included in the provision for credit losses.
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No definition available.
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| - Definition
Reserve for unfunded loan commitments and letters of credit.
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No definition available.
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|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of reduction of allowance reserve for credit loss arising from sale of loan and lease portfolios.
+ References
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                           |
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| - Definition
A valuation allowance for financing receivables that are expected to be uncollectible.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            |
|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.
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| - Definition
Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.
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| - Definition
Amount of recovery of financing receivables doubtful of collection that were previously charged off.
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| - Definition
A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.
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No definition available.
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| - Definition
Amount of direct write-downs of financing receivables charged against the allowance.
+ References
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| - Definition
The balance of financing receivables that were collectively evaluated for impairment.
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| - Definition
The balance of financing receivables that were individually evaluated for impairment.
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| - Definition
Amount representing an agreement for an unconditional promise by the maker to pay the entity (holder) a definite sum of money at a future date. Such amount may include accrued interest receivable in accordance with the terms of the note. The note also may contain provisions and related items including a discount or premium, payable on demand, secured, or unsecured, interest bearing or noninterest bearing, among a myriad of other features and characteristics. Excludes amounts related to receivables held-for-sale.
+ References
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| - Definition
Amount of expense related to estimated loss from loan and lease transactions.
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