| **BASIS OF PRESENTATION AND ACCOUNTING POLICIES (General) (Details) $ in Thousands**                                                                                  | 3 Months Ended | 9 Months Ended |              |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------|----------------|----------------|--------------|
||
| **Noncontrolling Interest [Line Items]**                                                                                                                              |                |           |         |   |
| Deposits                                                                                                                                                              |                | $ 66,239,968   | $ 66,239,968 | $ 61,511,380 |
| Loans held-for-sale (LHFS)                                                                                                                                            | [1]            | 2,480,809      | 2,480,809    | $ 1,283,278 |
| Affiliated Entity | SBNA                                                                                                                                              |                |           |         |   |
| **Noncontrolling Interest [Line Items]**                                                                                                                              |                |           |         |   |
| Deposits                                                                                                                                                              |                | 471,000        | 471,000      |   |
| Loans held-for-sale (LHFS)                                                                                                                                            |                | 102,000        | $ 102,000    |   |
| Gain on sale of financing receivable                                                                                                                                  |                | $ 30,900       |         |   |
| SC                                                                                                                                                                    |                |           |         |   |
| **Noncontrolling Interest [Line Items]**                                                                                                                              |                |           |         |   |
| Ownership percentage by parent                                                                                                                                        |                | 71.60%         | 71.60%       |   |
| Percentage owned by noncontrolling shareholders                                                                                                                       |                | 28.40%         | 28.40%       |   |
| SC                                                                                                                                                                    |                |           |         |   |
| **Noncontrolling Interest [Line Items]**                                                                                                                              |                |           |         |   |
| Financing contract term                                                                                                                                               |                |           | 10 years     |   |
| First Commonwealth Bank | Affiliated Entity | SBNA | Disposed of by Sale                                                                                              |                |           |         |   |
| **Noncontrolling Interest [Line Items]**                                                                                                                              |                |           |         |   |
| Number of bank branches | branch                                                                                                                                      |                | 14             | 14           |   |
| Number of ATMs to be sold | atm                                                                                                                                       |                | 4              | 4            |   |
|                                                                                                                                                                       |
| [1]Includes $437.9 million and $209.5 million of loans recorded at the fair value option ("FVO") at September 30, 2019 and December 31, 2018, respectively. |

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Number Of ATMs
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| X                                                                                                                                                                                                                           |
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Number Of Bank Branches
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| - Definition
The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.
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| - Definition
Amount of gain (loss) on sale of financing receivable.
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| - Definition
Amount, after allowance for bad debt, of loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities.
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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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The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.
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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.
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