Fair Value - Fair Value Option (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Fair Value Inputs, Quantitative Information [Line Items]
Total multifamily mortgage loans held for investment, at amortized cost	$ 5,464	$ 3,744
Fair value of nonaccrual loans	$ 30	31
Serious delinquency: days past due	90 days
Fair value of loans that are 90 days past due	$ 26	25
Changes in fair value, gain (loss)	90	1,821	$ 1,304
Fannie Mae
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	256	385
Consolidated Trusts
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	15,060	13,292
Loans
Fair Value Inputs, Quantitative Information [Line Items]
Total multifamily mortgage loans held for investment, at amortized cost	5,464	3,744
Loans, unpaid principal balance	5,808	4,079
Changes in fair value, gain (loss)	290	(26)	108
Long-term Debt
Fair Value Inputs, Quantitative Information [Line Items]
Changes in fair value, gain (loss)	(702)	59	$ (308)
Long-term Debt \| Fannie Mae
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	256	385
Debt, unpaid principal balance	250	383
Long-term Debt \| Consolidated Trusts
Fair Value Inputs, Quantitative Information [Line Items]
Long-term debt	15,060	13,292
Debt, unpaid principal balance	$ 15,516	$ 13,766

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.

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For each line item in the statement of financial position, the amounts of gains and losses from fair value changes included in earnings.

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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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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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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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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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