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DEBT SECURITIES - Narrative (Details) - USD ($) |  | 3 Months Ended | 9 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Jan. 01, 2022 | Sep. 30, 2025 | Sep. 30, 2024 | Mar. 31, 2024 | Sep. 30, 2025 | Sep. 30, 2024 | Jun. 30, 2025 | Dec. 31, 2024 | Jun. 30, 2024 | Dec. 31, 2023
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |  |
Debt securities, available-for-sale and held to maturity, accrued interest, after allowance for credit loss |  | $ 19,600,000 |  |  | $ 19,600,000 |  |  | $ 15,900,000 |  |
Debt securities, available-for-sale, accrued interest, after allowance for credit loss |  | 17,400,000 |  |  | 17,400,000 |  |  | 13,600,000 |  |
Debt securities, held-to-maturity, accrued interest, after allowance for credit loss |  | 2,200,000 |  |  | 2,200,000 |  |  | 2,400,000 |  |
Trading securities |  | 50,357,000 |  |  | 50,357,000 |  |  | 0 |  |
Trading gains (losses) recorded in servicing income |  | 98,000 | $ 0 |  | 98,000 | $ 0 |  |  |  |
Debt securities, available-for-sale, sold at par value |  |  |  | $ 1,800,000,000 |  |  |  |  |  |
Realized loss on AFS securities |  | 0 | 0 | 207,200,000 | 923,000 | 207,203,000 |  |  |  |
Purchases |  |  |  | 1,600,000,000 | 561,139,000 | 2,154,513,000 |  |  |  |
Realized gains on AFS securities |  | 155,000 | 0 | $ 0 | 5,215,000 | 0 |  |  |  |
Tax exempt interest income on available-for-sale securities |  | 1,900,000 | 776,000 |  | 3,400,000 | 2,400,000 |  |  |  |
Equity |  | 2,774,134,000 | 2,299,264,000 |  | 2,774,134,000 | 2,299,264,000 | $ 2,416,617,000 | 2,301,868,000 | $ 2,244,042,000 | $ 2,235,605,000
Unrealized loss accreted to interest income |  | 627,000 | 648,000 |  | 1,900,000 | 1,900,000 |  |  |  |
Debt securities, available-for-sale, transfer to held-to-maturity, gain (loss) |  | 0 |  |  | 0 |  |  |  |  |
Allowance for credit loss on debt securities, available-for-sale |  | 0 |  |  | 0 |  |  |  |  |
Allowance for credit loss on debt securities, held-to-maturity |  |  |  |  |  |  |  | 0 |  |
Asset Pledged as Collateral | Securities Sold under Agreements to Repurchase |  |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |  |
Public funds included in deposits, pledged collateral, amount |  | 1,500,000,000 |  |  | 1,500,000,000 |  |  |  |  |
Asset Pledged as Collateral | Federal Reserve Bank Advances | Equity Securities |  |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |  |
Public funds included in deposits, pledged collateral, amount |  |  |  |  |  |  |  | 3,000,000,000.0 |  |
Securities |  |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |  |
Equity |  | (13,305,000) | $ (18,472,000) |  | (13,305,000) | $ (18,472,000) | $ (35,945,000) | (64,058,000) | $ (63,768,000) | $ (199,625,000)
Residential and Commercial Portfolio Segment | Residential and Commercial Mortgage |  |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |  |
Transfers of securities securities available-for-sale to held-to-maturity | $ 1,700,000,000 |  |  |  |  |  |  |  |  |
Residential and Commercial Portfolio Segment | Residential and Commercial Mortgage | Securities |  |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |  |
Other comprehensive income, amount remaining of debt securities available for sale transfer to held to maturity, before tax | 23,500,000 |  |  |  |  |  |  |  |  |
Other comprehensive income, amount remaining of debt securities available for sale transfer to held to maturity, net of deferred taxes | $ 16,700,000 |  |  |  |  |  |  |  |  |
US Treasury Notes Securities |  |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |  |
Trading securities |  | $ 50,400,000 |  |  | $ 50,400,000 |  |  |  |  |
US Treasury Notes Securities | Designated as Hedging Instrument |  |  |  |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |  |  |  |
Trading securities |  |  |  |  |  |  |  | $ 0 |  |

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