Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2023	Nov. 03, 2023
Document Information [Line Items]
Entity Central Index Key	0000719402
Entity Registrant Name	FIRST NATIONAL CORP /VA/
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Period Focus	Q3
Document Fiscal Year Focus	2023
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2023
Document Transition Report	false
Entity File Number	1-38874
Entity Incorporation, State or Country Code	VA
Entity Tax Identification Number	54-1232965
Entity Address, Address Line One	112 West King Street
Entity Address, City or Town	Strasburg
Entity Address, State or Province	VA
Entity Address, Postal Zip Code	22657
City Area Code	540
Local Phone Number	465-9121
Title of 12(b) Security	Common stock, par value $1.25 per share
Trading Symbol	FXNC
Security Exchange Name	NASDAQ
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
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		6,260,934