Fair Value - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Fair Value Measurement [Domain]
Financial assets:
Derivative assets, gross amount offset	$ (136)	$ (199)
Financial liabilities:
Derivative liabilities, gross amount offset	(1,299)	(1,242)
Available-for-sale securities	12,424	375
Derivative assets at fair value	352	177
Derivative assets, gross amount offset	(136)	(199)
Derivative liabilities at fair value	676	152
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash, including restricted cash	45,264	42,583
Securities purchased under agreements to resell	0	0
Trading securities	44,406	55,205
Available-for-sale securities	11,906	0
Mortgage loans held for sale	0	0
Mortgage loans held for investment, net of allowance for loan losses	0	0
Advances to lenders	0	0
Derivative assets at fair value	0	0
Guaranty assets	0	0
Total financial assets	101,576	97,788
Financial liabilities:
Derivative liabilities at fair value	0	0
Guaranty obligations	0	0
Total financial liabilities	0	0
Significant Other Observable Inputs (Level 2)
Financial assets:
Cash, including restricted cash	0	0
Securities purchased under agreements to resell	38,199	45,650
Trading securities	18,664	14,282
Available-for-sale securities	187	34
Mortgage loans held for sale	22	23
Mortgage loans held for investment, net of allowance for loan losses	3,607,231	3,656,465
Advances to lenders	3,509	3,595
Derivative assets at fair value	418	304
Guaranty assets	0	0
Total financial assets	3,668,230	3,720,353
Financial liabilities:
Derivative liabilities at fair value	1,959	1,387
Guaranty obligations	0	0
Total financial liabilities	3,807,829	3,832,394
Significant Unobservable Inputs (Level 3)
Financial assets:
Cash, including restricted cash	0	0
Securities purchased under agreements to resell	0	0
Trading securities	26	27
Available-for-sale securities	331	341
Mortgage loans held for sale	191	201
Mortgage loans held for investment, net of allowance for loan losses	163,972	137,864
Advances to lenders	0	0
Derivative assets at fair value	70	72
Guaranty assets	179	172
Total financial assets	164,769	138,677
Financial liabilities:
Derivative liabilities at fair value	16	7
Guaranty obligations	52	54
Total financial liabilities	897	898
Fannie Mae
Financial liabilities:
Long-term debt	265	256
Fannie Mae \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial liabilities:
Short-term debt:	0	0
Long-term debt	0	0
Fannie Mae \| Significant Other Observable Inputs (Level 2)
Financial liabilities:
Short-term debt:	20,606	24,548
Long-term debt	131,354	104,784
Fannie Mae \| Significant Unobservable Inputs (Level 3)
Financial liabilities:
Short-term debt:	0	0
Long-term debt	599	602
Consolidated Trusts
Financial liabilities:
Long-term debt	13,707	15,060
Consolidated Trusts \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial liabilities:
Long-term debt	0	0
Consolidated Trusts \| Significant Other Observable Inputs (Level 2)
Financial liabilities:
Long-term debt	3,653,910	3,701,675
Consolidated Trusts \| Significant Unobservable Inputs (Level 3)
Financial liabilities:
Long-term debt	230	235
Carrying Value
Financial assets:
Cash, including restricted cash	45,264	42,583
Securities purchased under agreements to resell	38,199	45,650
Trading securities	63,096	69,514
Available-for-sale securities	12,424	375
Mortgage loans held for sale	199	209
Mortgage loans held for investment, net of allowance for loan losses	4,115,101	4,119,104
Advances to lenders	3,509	3,595
Derivative assets at fair value	352	177
Guaranty assets	96	90
Total financial assets	4,278,240	4,281,297
Financial liabilities:
Derivative liabilities at fair value	676	152
Guaranty obligations	101	96
Total financial liabilities	4,173,579	4,180,677
Carrying Value \| Fannie Mae
Financial liabilities:
Short-term debt:	20,602	24,538
Long-term debt	129,836	102,751
Carrying Value \| Consolidated Trusts
Financial liabilities:
Long-term debt	4,022,364	4,053,140
Estimated Fair Value
Financial assets:
Cash, including restricted cash	45,264	42,583
Securities purchased under agreements to resell	38,199	45,650
Trading securities	63,096	69,514
Available-for-sale securities	12,424	375
Mortgage loans held for sale	213	224
Mortgage loans held for investment, net of allowance for loan losses	3,771,203	3,794,329
Advances to lenders	3,509	3,595
Derivative assets at fair value	352	177
Guaranty assets	179	172
Total financial assets	3,934,439	3,956,619
Financial liabilities:
Derivative liabilities at fair value	676	152
Guaranty obligations	52	54
Total financial liabilities	3,807,427	3,832,050
Estimated Fair Value \| Fannie Mae
Financial liabilities:
Short-term debt:	20,606	24,548
Long-term debt	131,953	105,386
Estimated Fair Value \| Consolidated Trusts
Financial liabilities:
Long-term debt	$ 3,654,140	$ 3,701,910

This element represents the portion of the balance sheet assertion valued at fair value by the entity 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. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. The carrying amounts of cash and cash equivalent items which are restricted as to withdrawal or usage. Restrictions may include legally restricted deposits held as compensating balances against borrowing arrangements, contracts entered into with others, or entity statements of intention with regard to particular deposits; however, time deposits and short-term certificates of deposit are not generally included in legally restricted deposits. Excludes compensating balance arrangements that are not agreements which legally restrict the use of cash amounts shown on the balance sheet. This element is for unclassified presentations; for classified presentations there is a separate and distinct element.

No definition available.