Fair Value - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2025	Dec. 31, 2024
Fair Value Measurement [Domain]
Financial assets:
Derivative assets, gross amount offset	$ (399)	$ (362)
Financial liabilities:
Derivative liabilities, gross amount offset	(1,893)	(2,367)
Available-for-sale securities	445	469
Mortgage loans held for investment, net of allowance for loan losses	4,508	3,744
Derivative assets at fair value	127	179
Derivative assets, gross amount offset	(399)	(362)
Derivative liabilities at fair value	157	154
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	38,072	38,536
Securities purchased under agreements to resell	0	0
Trading securities	77,865	77,610
Available-for-sale securities	0	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	115,937	116,146
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 and cash equivalents, including restricted cash and cash equivalents	39,725	40,275
Securities purchased under agreements to resell	31,769	15,975
Trading securities	1,011	1,090
Available-for-sale securities	40	42
Mortgage loans held for sale	485	130
Mortgage loans held for investment, net of allowance for loan losses	3,562,659	3,496,803
Advances to lenders	1,848	1,825
Derivative assets at fair value	472	487
Guaranty assets	0	0
Total financial assets	3,638,009	3,556,627
Financial liabilities:
Derivative liabilities at fair value	2,031	2,506
Guaranty obligations	0	0
Total financial liabilities	3,775,978	3,700,088
Significant Unobservable Inputs (Level 3)
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	0	0
Securities purchased under agreements to resell	0	0
Trading securities	26	28
Available-for-sale securities	405	427
Mortgage loans held for sale	312	258
Mortgage loans held for investment, net of allowance for loan losses	132,222	127,763
Advances to lenders	0	0
Derivative assets at fair value	54	54
Guaranty assets	158	160
Total financial assets	133,177	128,690
Financial liabilities:
Derivative liabilities at fair value	19	15
Guaranty obligations	58	60
Total financial liabilities	934	916
Fannie Mae
Financial liabilities:
Long-term debt:	358	385
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:	11,042	11,193
Long-term debt:	127,301	129,152
Fannie Mae \| Significant Unobservable Inputs (Level 3)
Financial liabilities:
Short-term debt:	0	0
Long-term debt:	592	567
Consolidated Trusts
Financial liabilities:
Long-term debt:	14,977	13,292
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:	3,635,604	3,557,237
Consolidated Trusts \| Significant Unobservable Inputs (Level 3)
Financial liabilities:
Long-term debt:	265	274
Carrying Value
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	77,797	78,811
Securities purchased under agreements to resell	31,769	15,975
Trading securities	78,902	78,728
Available-for-sale securities	445	469
Mortgage loans held for sale	775	373
Mortgage loans held for investment, net of allowance for loan losses	4,126,401	4,137,633
Advances to lenders	1,848	1,825
Derivative assets at fair value	127	179
Guaranty assets	61	64
Total financial assets	4,318,125	4,314,057
Financial liabilities:
Derivative liabilities at fair value	157	154
Guaranty obligations	67	69
Total financial liabilities	4,228,882	4,228,320
Carrying Value \| Fannie Mae
Financial liabilities:
Short-term debt:	11,041	11,188
Long-term debt:	125,777	128,234
Carrying Value \| Consolidated Trusts
Financial liabilities:
Long-term debt:	4,091,840	4,088,675
Estimated Fair Value
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	77,797	78,811
Securities purchased under agreements to resell	31,769	15,975
Trading securities	78,902	78,728
Available-for-sale securities	445	469
Mortgage loans held for sale	797	388
Mortgage loans held for investment, net of allowance for loan losses	3,694,881	3,624,566
Advances to lenders	1,848	1,825
Derivative assets at fair value	127	179
Guaranty assets	158	160
Total financial assets	3,886,724	3,801,101
Financial liabilities:
Derivative liabilities at fair value	157	154
Guaranty obligations	58	60
Total financial liabilities	3,775,019	3,698,637
Estimated Fair Value \| Fannie Mae
Financial liabilities:
Short-term debt:	11,042	11,193
Long-term debt:	127,893	129,719
Estimated Fair Value \| Consolidated Trusts
Financial liabilities:
Long-term debt:	$ 3,635,869	$ 3,557,511

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.