Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Feb. 01, 2024	Jun. 30, 2023
Document Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	0-50231
Entity Registrant Name	FEDERAL NATIONAL MORTGAGE ASSOCIATION FANNIE MAE
Entity Tax Identification Number	52-0883107
Entity Address, Address Line One	1100 15th Street, NW
Entity Address, City or Town	Washington,
Entity Address, State or Province	DC
Entity Address, Postal Zip Code	20005
City Area Code	800
Local Phone Number	232-6643
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Document Financial Statement Error Correction [Flag]	false
Entity Shell Company	false
Entity Public Float			$ 510
Entity Common Stock, Shares Outstanding		1,158,087,567
Entity Central Index Key	0000310522
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Entity Incorporation, State or Country Code	X1
Amendment Flag	false
Common Stock
Document Information [Line Items]
Title of 12(g) Security	Common Stock, without par value
Series T
Document Information [Line Items]
Title of 12(g) Security	8.25% Non-Cumulative Preferred Stock, Series T, stated value $25 per share
Series S
Document Information [Line Items]
Title of 12(g) Security	Fixed-to-Floating Rate Non-Cumulative Preferred Stock, Series S, stated value $25 per share
Series R
Document Information [Line Items]
Title of 12(g) Security	7.625% Non-Cumulative Preferred Stock, Series R, stated value $25 per share
Series Q
Document Information [Line Items]
Title of 12(g) Security	6.75% Non-Cumulative Preferred Stock, Series Q, stated value $25 per share
Series P
Document Information [Line Items]
Title of 12(g) Security	Variable Rate Non-Cumulative Preferred Stock, Series P, stated value $25 per share
Series O
Document Information [Line Items]
Title of 12(g) Security	Variable Rate Non-Cumulative Preferred Stock, Series O, stated value $50 per share
Convertible Series 2004-1
Document Information [Line Items]
Title of 12(g) Security	5.375% Non-Cumulative Convertible Series 2004-1 Preferred Stock, stated value $100,000 per share
Series N
Document Information [Line Items]
Title of 12(g) Security	5.50% Non-Cumulative Preferred Stock, Series N, stated value $50 per share
Series M
Document Information [Line Items]
Title of 12(g) Security	4.75% Non-Cumulative Preferred Stock, Series M, stated value $50 per share
Series L
Document Information [Line Items]
Title of 12(g) Security	5.125% Non-Cumulative Preferred Stock, Series L, stated value $50 per share
Series I
Document Information [Line Items]
Title of 12(g) Security	5.375% Non-Cumulative Preferred Stock, Series I, stated value $50 per share
Series H
Document Information [Line Items]
Title of 12(g) Security	5.81% Non-Cumulative Preferred Stock, Series H, stated value $50 per share
Series G
Document Information [Line Items]
Title of 12(g) Security	Variable Rate Non-Cumulative Preferred Stock, Series G, stated value $50 per share
Series F
Document Information [Line Items]
Title of 12(g) Security	Variable Rate Non-Cumulative Preferred Stock, Series F, stated value $50 per share
Series E
Document Information [Line Items]
Title of 12(g) Security	5.10% Non-Cumulative Preferred Stock, Series E, stated value $50 per share
Series D
Document Information [Line Items]
Title of 12(g) Security	5.25% Non-Cumulative Preferred Stock, Series D, stated value $50 per share