Fair Value - Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Fair Value Measurement [Domain]
Financial assets:
Netting Adjustment	$ (283)	$ (154)
Financial liabilities:
Netting Adjustment	(3,200)	(4,662)
Total Fair Value	564	696
Mortgage loans	3,315	3,645
Derivative assets at fair value	202	175
Netting Adjustment	(283)	(154)
Derivative liabilities at fair value	140	168
Fannie Mae
Financial liabilities:
Debt:	761	1,161
Consolidated Trusts
Financial liabilities:
Debt:	14,343	16,260
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	33,981	32,991
Securities purchased under agreements to resell	0	0
Trading securities	47,764	46,898
Total Fair Value	0	0
Mortgage loans held for sale	0	0
Mortgage loans	0	0
Advances to lenders	0	0
Derivative assets at fair value	0	0
Guaranty assets and buy-ups	0	0
Total assets at fair value	81,745	79,889
Financial liabilities:
Derivative liabilities at fair value	0	0
Guaranty obligations	0	0
Total financial liabilities	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Fannie Mae
Financial liabilities:
Short-term debt:	0	0
Debt:	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) \| Consolidated Trusts
Financial liabilities:
Debt:	0	0
Significant Other Observable Inputs (Level 2)
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	34,725	54,850
Securities purchased under agreements to resell	30,700	14,565
Trading securities	4,762	3,184
Total Fair Value	50	62
Mortgage loans held for sale	93	48
Mortgage loans	3,571,555	3,437,979
Advances to lenders	1,389	1,502
Derivative assets at fair value	395	300
Guaranty assets and buy-ups	0	0
Total assets at fair value	3,643,669	3,512,490
Financial liabilities:
Derivative liabilities at fair value	3,327	4,764
Guaranty obligations	0	0
Total financial liabilities	3,760,502	3,648,996
Significant Other Observable Inputs (Level 2) \| Fannie Mae
Financial liabilities:
Short-term debt:	17,317	10,208
Debt:	106,701	122,066
Significant Other Observable Inputs (Level 2) \| Consolidated Trusts
Financial liabilities:
Debt:	3,633,157	3,511,958
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	47
Total Fair Value	514	634
Mortgage loans held for sale	2,196	2,029
Mortgage loans	130,022	171,857
Advances to lenders	0	0
Derivative assets at fair value	90	29
Guaranty assets and buy-ups	155	166
Total assets at fair value	133,003	174,762
Financial liabilities:
Derivative liabilities at fair value	13	66
Guaranty obligations	65	66
Total financial liabilities	976	42,840
Significant Unobservable Inputs (Level 3) \| Fannie Mae
Financial liabilities:
Short-term debt:	0	0
Debt:	605	558
Significant Unobservable Inputs (Level 3) \| Consolidated Trusts
Financial liabilities:
Debt:	293	42,150
Carrying value
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	68,706	87,841
Securities purchased under agreements to resell	30,700	14,565
Trading securities	52,552	50,129
Total Fair Value	564	696
Mortgage loans held for sale	2,149	2,033
Mortgage loans	4,133,482	4,112,403
Advances to lenders	1,389	1,502
Derivative assets at fair value	202	175
Guaranty assets and buy-ups	73	87
Total assets at fair value	4,289,817	4,269,431
Financial liabilities:
Derivative liabilities at fair value	140	168
Guaranty obligations	79	94
Total financial liabilities	4,222,937	4,222,150
Carrying value \| Fannie Mae
Financial liabilities:
Short-term debt:	17,314	10,204
Debt:	106,751	123,964
Carrying value \| Consolidated Trusts
Financial liabilities:
Debt:	4,098,653	4,087,720
Estimate of fair value
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	68,706	87,841
Securities purchased under agreements to resell	30,700	14,565
Trading securities	52,552	50,129
Total Fair Value	564	696
Mortgage loans held for sale	2,289	2,077
Mortgage loans	3,701,577	3,609,836
Advances to lenders	1,389	1,502
Derivative assets at fair value	202	175
Guaranty assets and buy-ups	155	166
Total assets at fair value	3,858,134	3,766,987
Financial liabilities:
Derivative liabilities at fair value	140	168
Guaranty obligations	65	66
Total financial liabilities	3,758,278	3,687,174
Estimate of fair value \| Fannie Mae
Financial liabilities:
Short-term debt:	17,317	10,208
Debt:	107,306	122,624
Estimate of fair value \| Consolidated Trusts
Financial liabilities:
Debt:	$ 3,633,450	$ 3,554,108

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.