Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2024	Mar. 21, 2025	Jun. 30, 2024
Document and Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2024
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 Common Stock, Shares Outstanding		5,559,473
Entity Central Index Key	0002012726
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	FY
Amendment Flag	false
Auditor Name	Elliott Davis, LLC
Auditor Location	Franklin, Tennessee
Auditor Firm ID	149
Entity Public Float			$ 0