v3.26.1
Document and Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Mar. 24, 2026
Jun. 30, 2025
Document and Entity Information        
Document Type 10-K      
Document Annual Report true      
Document Period End Date Dec. 31, 2025      
Document Transition Report false      
Entity File Number 001-42198      
Entity Registrant Name Fifth District Bancorp, Inc.      
Entity Incorporation, State or Country Code MD      
Entity Tax Identification Number 99-1897673      
Entity Address, Address Line One 4000 General DeGaulle Drive      
Entity Address, City or Town New Orleans      
Entity Address, State or Province LA      
Entity Address, Postal Zip Code 70114      
City Area Code 504      
Local Phone Number 362-7544      
Title of 12(b) Security Common Stock, par value $0.01 per share      
Trading Symbol FDSB      
Security Exchange Name NASDAQ      
Entity Well-known Seasoned Issuer No      
Entity Voluntary Filers No      
Entity Current Reporting Status Yes      
Entity Interactive Data Current Yes      
Entity Filer Category Non-accelerated Filer      
Entity Small Business true      
Entity Emerging Growth Company true      
Entity Ex Transition Period false      
ICFR Auditor Attestation Flag false      
Document Financial Statement Error Correction [Flag] false      
Entity Shell Company false      
Entity Public Float       $ 58,211,478
Entity Common Stock, Shares Outstanding     5,293,801  
Documents Incorporated by Reference [Text Block]

Portions of the Definitive Proxy Statement for the 2026 Annual Meeting of Stockholders are incorporated by reference in Part III of the Form 10-K.

      
Entity Central Index Key 0002012726      
Current Fiscal Year End Date --12-31      
Document Fiscal Year Focus 2025      
Document Fiscal Period Focus FY      
Amendment Flag false      
Auditor Name EISNERAMPER LLP Elliott Davis, LLC    
Auditor Location Metairie, Louisiana Franklin, Tennessee    
Auditor Firm ID 274 149