Fair Value - Fair Value Option (Details) - USD ($) $ in Millions	9 Months Ended
Sep. 30, 2026	Dec. 31, 2025
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgage loans held for investment, net of allowance for loan losses	$ 6,309	$ 5,464
Fair value of nonaccrual loans	$ 30	30
Serious delinquency, days past due	90 days
Fair value of loans that are 90 days or more past due	$ 25	26
Fannie Mae
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term debt	235	256
Consolidated Trusts
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term debt	14,728	15,060
Loans
Fair Value, Option, Quantitative Disclosures [Line Items]
Mortgage loans held for investment, net of allowance for loan losses	6,309	5,464
Loans, unpaid principal balance	7,242	5,808
Long-term Debt \| Fannie Mae
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term debt	235	256
Long-term debt, unpaid principal balance	250	250
Long-term Debt \| Consolidated Trusts
Fair Value, Option, Quantitative Disclosures [Line Items]
Long-term debt	14,728	15,060
Long-term debt, unpaid principal balance	$ 16,346	$ 15,516

Represents principal amount outstanding of loans held for investment.

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- Definition

Represents the number of days past due required for a loan to be considered seriously delinquent.

+ References

No definition available.

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- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

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- Definition

This item represents the aggregate fair value of loans held as assets that are 90 days or more past due for which the fair value option has been elected.

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- Definition

This item represents the aggregate fair value of loans held as assets that are in nonaccrual status for which the fair value option has been elected, if the entity's policy is to recognize interest income separately from other changes in fair value.

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- Definition

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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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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