| Document and Entity Information | Oct. 29, 2021 |
| Cover [Abstract] | |
| Entity Registrant Name | 1895 Bancorp of Wisconsin, Inc. /MD/ |
| Amendment Flag | false |
| Entity Central Index Key | 0001847360 |
| Document Type | 8-K |
| Document Period End Date | Oct. 29, 2021 |
| Entity Incorporation State Country Code | MD |
| Entity File Number | 001-40609 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.01 per share |
| Trading Symbol | BCOW |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
