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SECURITIES - Component of Agency Mortgage-Backed Securities Portfolio by Issuing Agency Concentration (Details) - Agency Mortgage-Backed Securities - USD ($) $ in Thousands | Sep. 30, 2023 | Dec. 31, 2022
--- | --- | ---
Mortgage-Backed Securities Portfolio [Line Items] |  |
Mortgage-backed securities | $ 66,591,536 | $ 62,274,895
Fannie Mae |  |
Mortgage-Backed Securities Portfolio [Line Items] |  |
Mortgage-backed securities | 60,747,738 | 54,043,015
Freddie Mac |  |
Mortgage-Backed Securities Portfolio [Line Items] |  |
Mortgage-backed securities | 5,790,893 | 8,174,080
Ginnie Mae |  |
Mortgage-Backed Securities Portfolio [Line Items] |  |
Mortgage-backed securities | $ 52,905 | $ 57,800

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- Definition The fair value as of the balance sheet date of firm holdings in mortgages, mortgage backed securities (investment instruments that represent ownership of an undivided interest in a group of mortgages, where principal and interest from the individual mortgages are used to pay investors' principal and interest on the mortgage backed security) and asset-backed securities that are primarily paid from the cash flows of a discrete pool of receivables or other financial assets (such as credit-card receivables), either fixed or revolving, that by their terms convert into cash within a finite time period. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 45 -Paragraph 2 -Publisher FASB -URI https://asc.fasb.org//1943274/2147481961/940-320-45-2 + Details
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