v3.25.4
Cover Page - USD ($)
$ in Billions
 12 Months Ended
Dec. 31, 2025
Jan. 29, 2026
Jun. 30, 2025
Document Information [Line Items]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2025    
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 Large 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     $ 11.0
Entity Common Stock, Shares Outstanding   1,158,087,567  
Entity Central Index Key 0000310522    
Document Fiscal Year Focus 2025    
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