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Document And Entity Information - USD ($)
 12 Months Ended
Dec. 31, 2024
Mar. 21, 2025
Jun. 30, 2024
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 FY    
Document Fiscal Year Focus 2024    
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2024    
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 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    
ICFR Auditor Attestation Flag false    
Document Financial Statement Error Correction [Flag] false    
Entity Shell Company false    
Entity Public Float     $ 77,200,000
Entity Common Stock, Shares Outstanding   8,986,696  
Auditor Name Yount, Hyde & Barbour, P.C    
Auditor Firm ID 613    
Auditor Location Winchester, Virginia