Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Document And Entity Information [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
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
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
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		4,419,107
Entity Central Index Key	0000723646
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false