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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) $ in Millions |  |  | 9 Months Ended
--- | --- | --- | ---
Apr. 30, 2024 | Feb. 10, 2023 USD ($) branch | Sep. 30, 2024 segment
Asset Acquisition [Line Items] |  |  |
Number of reporting segments | segment |  |  | 1
HomeStreet Bank | FirstSun Bank |  |  |
Asset Acquisition [Line Items] |  |  |
Equity exchange ratio | 0.3867 |  |
California | Three Branches Purchase |  |  |
Asset Acquisition [Line Items] |  |  |
Number of branches purchased | branch |  | 3 |
Deposit liabilities assumed |  | $ 376 |
Acquired receivables |  | 21 |
Goodwill |  | 12 |
Intangible assets acquired |  | $ 11 |

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