| **GOODWILL AND OTHER INTANGIBLES (Narrative) (Details) - USD ($) $ in Thousands** | 3 Months Ended | 9 Months Ended |
|-----------------------------------------------------------------------------------|----------------|----------------|
||
| **Goodwill [Line Items]**                                                         |           |           |   |   |   |   |
| Impairment during the period                                                      |           |           |   |   | $ 0 |   |
| Intangibles subject to amortization                                               | $ 614,419      |           | $ 649,276 |   | 614,419 |   |
| Accumulated amortization                                                          | 536,185        |           | 483,325 |   | 536,185 |   |
| Amortization of intangibles                                                       | 17,174         |           |   | $ 19,245 | 52,860 | $ 59,144 |
| Consumer and Business Banking                                                     |           |           |   |   |   |   |
| **Goodwill [Line Items]**                                                         |           |           |   |   |   |   |
| Goodwill reallocated                                                              |           | $ 330,000      |   |   |   |   |
| Impairment during the period                                                      |           |           |   |   | 0 |   |
| Auto Finance & Business Banking                                               |           |           |   |   |   |   |
| **Goodwill [Line Items]**                                                         |           |           |   |   |   |   |
| Impairment during the period                                                      |           |           |   |   | 0 |   |
| Commercial Real Estate Banking                                                    |           |           |   |   |   |   |
| **Goodwill [Line Items]**                                                         |           |           |   |   |   |   |
| Goodwill reallocated                                                              |           | 870,400        |   |   |   |   |
| Commercial Banking                                                                |           |           |   |   |   |   |
| **Goodwill [Line Items]**                                                         |           |           |   |   |   |   |
| Goodwill reallocated                                                              |           | $ 115,900      |   |   |   |   |
| Impairment during the period                                                      |           |           |   |   | 0 |   |
| SC                                                                                |           |           |   |   |   |   |
| **Goodwill [Line Items]**                                                         |           |           |   |   |   |   |
| Impairment during the period                                                      |           |           | 4,500,000 |   | 0 |   |
| Core deposit intangibles and purchased credit card relationships                  |           |           |   |   |   |   |
| **Goodwill [Line Items]**                                                         |           |           |   |   |   |   |
| Intangibles subject to amortization                                               | 0              |           | 763 |   | 0 |   |
| Accumulated amortization                                                          | 295,842        |           | 295,079 |   | $ 295,842 |   |
| Intangible asset useful life                                                      |           |           |   |   | 10 years |   |
| Trade name                                                                        |           |           |   |   |   |   |
| **Goodwill [Line Items]**                                                         |           |           |   |   |   |   |
| Intangibles subject to amortization                                               | 17,400         |           |   |   | $ 17,400 |   |
| Accumulated amortization                                                          | 600            |           |   |   | 600 |   |
| Trade name                                                                        |           |           |   |   |   |   |
| **Goodwill [Line Items]**                                                         |           |           |   |   |   |   |
| Intangibles not subject to amortization                                           |           |           | 18,000 |   |   |   |
| Intermediate Holding Company                                                      |           |           |   |   |   |   |
| **Goodwill [Line Items]**                                                         |           |           |   |   |   |   |
| Intangibles subject to amortization                                               | 28,200         |           | 19,200 |   | 28,200 |   |
| Accumulated amortization                                                          | $ 59,900       |           | $ 68,900 |   | $ 59,900 |   |

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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
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Amortization and Impairment of Intangible Assets
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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.
+ References
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| - Definition
Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.
+ References
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| - Definition
Amount of loss from the write-down of an 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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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
Amount of transfers into (out of) an 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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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount of assets, excluding financial assets and goodwill, lacking physical substance and having a projected indefinite period of benefit.
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