| **LOANS AND ALLOWANCE FOR CREDIT LOSSES - Troubled Debt Restructuring Activity (Details) $ in Thousands** | 3 Months Ended | 6 Months Ended |             |
|-----------------------------------------------------------------------------------------------------------|----------------|----------------|-------------|
||
| **Financing Receivable, Modified [Line Items]**                                                           |           |           |        |
| Amortized Cost                                                                                            |           |           | $ 3,172,438 |
| Number of Contracts | contract                                                                            | 8,936          | 18,043         |        |
| Pre-TDR Recorded Investment                                                                               | $ 169,237      | $ 344,840      |        |
| Amortized Cost                                                                                            | $ 169,262      | $ 344,748      |        |
| **TDRs which Subsequently Defaulted**                                                                     |           |           |        |
| Number of Contracts | contract                                                                            | 1,112          | 3,035          |        |
| Recorded Investment                                                                                       | $ 22,708       | $ 86,868       |        |
| Commercial | CRE                                                                                          |           |           |        |
| **Financing Receivable, Modified [Line Items]**                                                           |           |           |        |
| Number of Contracts | contract                                                                            |           | 45             |        |
| Pre-TDR Recorded Investment                                                                               |           | $ 7,465        |        |
| Amortized Cost                                                                                            |           | $ 7,465        |        |
| Commercial | C&I loans                                                                                |           |           |        |
| **Financing Receivable, Modified [Line Items]**                                                           |           |           |        |
| Number of Contracts | contract                                                                            | 30             | 234            |        |
| Pre-TDR Recorded Investment                                                                               | $ 1,404        | $ 7,108        |        |
| Amortized Cost                                                                                            | $ 1,404        | $ 7,110        |        |
| Commercial | Multifamily loans                                                                            |           |           |        |
| **Financing Receivable, Modified [Line Items]**                                                           |           |           |        |
| Number of Contracts | contract                                                                            | 9              | 17             |        |
| Pre-TDR Recorded Investment                                                                               | $ 7,168        | $ 7,168        |        |
| Amortized Cost                                                                                            | $ 7,168        | $ 7,168        |        |
| Commercial | Other commercial                                                                             |           |           |        |
| **Financing Receivable, Modified [Line Items]**                                                           |           |           |        |
| Number of Contracts | contract                                                                            | 2              | 12             |        |
| Pre-TDR Recorded Investment                                                                               | $ 9            | $ 228          |        |
| Amortized Cost                                                                                            | $ 9            | $ 228          |        |
| **TDRs which Subsequently Defaulted**                                                                     |           |           |        |
| Number of Contracts                                                                                       | 1              | 1              |        |
| Recorded Investment                                                                                       | $ 11           | $ 11           |        |
| Consumer | Residential mortgages                                                                          |           |           |        |
| **Financing Receivable, Modified [Line Items]**                                                           |           |           |        |
| Number of Contracts | contract                                                                            | 3              | 19             |        |
| Pre-TDR Recorded Investment                                                                               | $ 488          | $ 4,970        |        |
| Amortized Cost                                                                                            | $ 493          | $ 4,970        |        |
| **TDRs which Subsequently Defaulted**                                                                     |           |           |        |
| Number of Contracts | contract                                                                            | 6              | 80             |        |
| Recorded Investment                                                                                       | $ 2,088        | $ 28,649       |        |
| Consumer | Home equity loans and lines of credit                                                          |           |           |        |
| **Financing Receivable, Modified [Line Items]**                                                           |           |           |        |
| Number of Contracts | contract                                                                            | 24             | 64             |        |
| Pre-TDR Recorded Investment                                                                               | $ 3,589        | $ 8,456        |        |
| Amortized Cost                                                                                            | $ 3,847        | $ 8,760        |        |
| **TDRs which Subsequently Defaulted**                                                                     |           |           |        |
| Number of Contracts | contract                                                                            | 6              | 35             |        |
| Recorded Investment                                                                                       | $ 546          | $ 4,947        |        |
| Consumer | RICs and auto loans                                                                            |           |           |        |
| **Financing Receivable, Modified [Line Items]**                                                           |           |           |        |
| Number of Contracts | contract                                                                            | 8,868          | 17,650         |        |
| Pre-TDR Recorded Investment                                                                               | $ 156,579      | $ 308,172      |        |
| Amortized Cost                                                                                            | $ 156,341      | $ 307,774      |        |
| **TDRs which Subsequently Defaulted**                                                                     |           |           |        |
| Number of Contracts | contract                                                                            | 1,094          | 2,903          |        |
| Recorded Investment                                                                                       | $ 19,959       | $ 53,008       |        |
| Consumer | Personal unsecured loans                                                                       |           |           |        |
| **Financing Receivable, Modified [Line Items]**                                                           |           |           |        |
| Number of Contracts | contract                                                                            |           | 1              |        |
| Pre-TDR Recorded Investment                                                                               |           | $ 23           |        |
| Amortized Cost                                                                                            |           | $ 23           |        |
| **TDRs which Subsequently Defaulted**                                                                     |           |           |        |
| Number of Contracts | contract                                                                            | 5              | 14             |        |
| Recorded Investment                                                                                       | $ 104          | $ 196          |        |
| Consumer | Other consumer                                                                                 |           |           |        |
| **Financing Receivable, Modified [Line Items]**                                                           |           |           |        |
| Number of Contracts | contract                                                                            |           | 1              |        |
| Pre-TDR Recorded Investment                                                                               |           | $ 1,250        |        |
| Amortized Cost                                                                                            |           | $ 1,250        |        |
| **TDRs which Subsequently Defaulted**                                                                     |           |           |        |
| Number of Contracts | contract                                                                            | 0              | 2              |        |
| Recorded Investment                                                                                       | $ 0            | $ 57           |        |
| Performing                                                                                                |           |           |        |
| **Financing Receivable, Modified [Line Items]**                                                           |           |           |        |
| Amortized Cost                                                                                            |           |           | 2,694,007   |
| Non-performing                                                                                            |           |           |        |
| **Financing Receivable, Modified [Line Items]**                                                           |           |           |        |
| Amortized Cost                                                                                            |           |           | $ 478,431   |

| X                                                                                                                                                                                                                                                                                                           |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Financing Receivable, Modifications, Subsequent Default [Abstract]
+ References
No definition available.
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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.
+ References
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| - Definition
Number of financing receivables that have been modified by troubled debt restructurings.
+ References
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amortized cost of financing receivable modified during period for debtor experiencing financial difficulty.
+ References
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| - Definition
Amount, before troubled debt restructuring, of financing receivable to be modified.
+ References
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| - Definition
Accumulated amortized cost of financing receivable modified for debtor experiencing financial difficulty.
+ References
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| - Definition
Number of financing receivable contracts modified as troubled debt restructuring within previous 12 months, with subsequent payment default.
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| - Definition
Amortized cost of financing receivable with payment default in current period and modified within previous 12 months preceding payment default for debtor experiencing financial difficulty.
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