| Document and Entity Information | Feb. 14, 2025 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Feb. 14, 2025 |
| Entity File Number | 001-40609 |
| Entity Registrant Name | 1895 BANCORP OF WISCONSIN, INC. |
| Entity Central Index Key | 0001847360 |
| Entity Incorporation, State or Country Code | MD |
| Entity Tax Identification Number | 61-1993378 |
| Entity Address, Address Line One | 7001 West Edgerton Avenue |
| Entity Address, City or Town | Greenfield |
| Entity Address, State or Province | WI |
| Entity Address, Postal Zip Code | 53220 |
| City Area Code | 414 |
| Local Phone Number | 421-8200 |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | BCOW |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
