| Document And Entity Information | Jan. 29, 2021 |
| Document And Entity Information [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Jan. 29, 2021 |
| Entity Registrant Name | FRANKLIN FINANCIAL SERVICES CORPORATION |
| Entity Incorporation, State or Country Code | PA |
| Entity File Number | 001-38884 |
| Entity Tax Identification Number | 25-1440803 |
| Entity Address, Address Line One | 20 South Main Street |
| Entity Address, City or Town | Chambersburg |
| Entity Address, State or Province | PA |
| Entity Address, Postal Zip Code | 17201 |
| City Area Code | 717 |
| Local Phone Number | 264-6116 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common stock |
| Trading Symbol | FRAF |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000723646 |
| Amendment Flag | false |
