| Document and Entity Information | Jul. 31, 2024 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jul. 31, 2024 |
| Entity File Number | 333-277776 |
| Entity Registrant Name | Fifth District Bancorp, Inc. |
| Entity Central Index Key | 0002012726 |
| 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 |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
