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GUARANTEES AND MORTGAGE REPURCHASE LIABILITY - Narrative (Details) - USD ($) | 3 Months Ended | 6 Months Ended |  |  |  |
--- | --- | --- | --- | --- | --- | ---
Jun. 30, 2021 | Jun. 30, 2020 | Jun. 30, 2021 | Jun. 30, 2020 | Mar. 31, 2021 | Dec. 31, 2020 | Mar. 31, 2020 | Dec. 31, 2019
Representations and warranties reserve for loan receivables |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Unfunded commitment balance of loans sold on a servicing-retained basis | $ 5,700,000,000 |  | $ 5,700,000,000 |  |  | $ 6,000,000,000.0 |  |
Reserve liability related to mortgage repurchase | 1,612,000 | $ 2,083,000 | 1,612,000 | $ 2,083,000 | $ 1,941,000 | 2,122,000 | $ 2,482,000 | $ 2,871,000
Loss sharing relationship |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Reserve liability related to multifamily DUS program | 700,000 |  | 700,000 |  |  | 2,100,000 |  |
Loss sharing relationship | Multifamily |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
UPB of loans sold through DUS | 1,900,000,000 |  | 1,900,000,000 |  |  | 1,800,000,000 |  |
Losses incurred - related to DUS | 0 | $ 0 | 0 | $ 0 |  |  |  |
Credit risk |  |  |  |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |  |  |  |
Reserve liability related to mortgage repurchase | $ 1,600,000 |  | $ 1,600,000 |  |  | $ 2,100,000 |  |

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- Definition Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=124440162&loc=d3e12069-110248 + Details
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