Fair Value - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Fair Value Measurement [Domain]
Financial assets:
Derivative assets, gross amount offset	$ (321)	$ (154)
Financial liabilities:
Derivative liabilities, gross amount offset	(4,241)	(4,662)
Total Fair Value	584	696
Mortgage loans held for investment, net of allowance for loan losses	3,207	3,645
Derivative assets at fair value	149	175
Derivative assets, gross amount offset	(321)	(154)
Derivative liabilities at fair value	225	168
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	34,649	32,991
Securities purchased under agreements to resell	0	0
Trading securities	48,634	46,898
Total Fair Value	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 and buy-ups	0	0
Total financial assets	83,283	79,889
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	47,150	54,850
Securities purchased under agreements to resell	22,850	14,565
Trading securities	2,630	3,184
Total Fair Value	169	62
Mortgage loans held for sale	588	48
Mortgage loans held for investment, net of allowance for loan losses	3,346,542	3,437,979
Advances to lenders	3,384	1,502
Derivative assets at fair value	417	300
Guaranty assets and buy-ups	0	0
Total financial assets	3,423,730	3,512,490
Financial liabilities:
Derivative liabilities at fair value	4,452	4,764
Guaranty obligations	0	0
Total financial liabilities	3,550,088	3,648,996
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	24	47
Total Fair Value	415	634
Mortgage loans held for sale	2,062	2,029
Mortgage loans held for investment, net of allowance for loan losses	123,867	171,857
Advances to lenders	0	0
Derivative assets at fair value	53	29
Guaranty assets and buy-ups	168	166
Total financial assets	126,589	174,762
Financial liabilities:
Derivative liabilities at fair value	14	66
Guaranty obligations	71	66
Total financial liabilities	884	42,840
Fannie Mae
Financial liabilities:
Long-term debt:	833	1,161
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:	14,238	10,208
Long-term debt:	109,706	122,066
Fannie Mae \| Significant Unobservable Inputs (Level 3)
Financial liabilities:
Short-term debt:	0	0
Long-term debt:	551	558
Consolidated Trusts
Financial liabilities:
Long-term debt:	14,210	16,260
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:	3,421,692	3,511,958
Consolidated Trusts \| Significant Unobservable Inputs (Level 3)
Financial liabilities:
Long-term debt:	248	42,150
Carrying Value
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	81,799	87,841
Securities purchased under agreements to resell	22,850	14,565
Trading securities	51,288	50,129
Total Fair Value	584	696
Mortgage loans held for sale	2,587	2,033
Mortgage loans held for investment, net of allowance for loan losses	4,131,301	4,112,403
Advances to lenders	3,384	1,502
Derivative assets at fair value	149	175
Guaranty assets and buy-ups	75	87
Total financial assets	4,294,017	4,269,431
Financial liabilities:
Derivative liabilities at fair value	225	168
Guaranty obligations	81	94
Total financial liabilities	4,232,068	4,222,150
Carrying Value \| Fannie Mae
Financial liabilities:
Short-term debt:	14,245	10,204
Long-term debt:	111,407	123,964
Carrying Value \| Consolidated Trusts
Financial liabilities:
Long-term debt:	4,106,110	4,087,720
Fair Value
Financial assets:
Cash and cash equivalents, including restricted cash and cash equivalents	81,799	87,841
Securities purchased under agreements to resell	22,850	14,565
Trading securities	51,288	50,129
Total Fair Value	584	696
Mortgage loans held for sale	2,650	2,077
Mortgage loans held for investment, net of allowance for loan losses	3,470,409	3,609,836
Advances to lenders	3,384	1,502
Derivative assets at fair value	149	175
Guaranty assets and buy-ups	168	166
Total financial assets	3,633,281	3,766,987
Financial liabilities:
Derivative liabilities at fair value	225	168
Guaranty obligations	71	66
Total financial liabilities	3,546,731	3,687,174
Fair Value \| Fannie Mae
Financial liabilities:
Short-term debt:	14,238	10,208
Long-term debt:	110,257	122,624
Fair Value \| Consolidated Trusts
Financial liabilities:
Long-term debt:	$ 3,421,940	$ 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.