| Cover | Jun. 14, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Entity Registrant Name | FEDERAL HOME LOAN BANK OF SAN FRANCISCO |
| Entity File Number | 000-51398 |
| Entity Tax Identification Number | 94-6000630 |
| Entity Address, Address Line One | 333 Bush Street, Suite 2700 |
| Entity Address, City or Town | San Francisco |
| Entity Address, State or Province | CA |
| Entity Address, Postal Zip Code | 94104 |
| City Area Code | (415) |
| Local Phone Number | 616-1000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Document Period End Date | Dec. 1, 2021 |
| Entity Central Index Key | 0001316944 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | X1 |
| Entity Emerging Growth Company | false |
