Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2020	Feb. 28, 2021	Jun. 30, 2020
Document And Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-38884
Entity Registrant Name	FRANKLIN FINANCIAL SERVICES CORPORATION
Entity Incorporation, State or Country Code	PA
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	17201-0819
City Area Code	717
Local Phone Number	264-6116
Title of 12(b) Security	Common Stock, par value $1.00 per share
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Trading Symbol	FRAF
Security Exchange Name	NASDAQ
ICFR Auditor Attestation	false
Entity Shell Company	false
Entity Public Float			$ 103,025,150
Entity Common Stock, Shares Outstanding		4,399,352
Entity Central Index Key	0000723646
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false