Document And Entity Information - shares
6 Months Ended
Jun. 30, 2019
Jul. 23, 2019
Cover page.    
Title of 12(b) Security Common Stock, no par value  
Entity Incorporation, State or Country Code VA  
Document Transition Report false  
Document Type 10-Q  
Document Quarterly Report true  
Entity File Number 001-15811  
Entity Address, Address Line One 4521 Highwoods Parkway  
Entity Address, City or Town Glen Allen  
Entity Address, State or Province VA  
Entity Address, Postal Zip Code 23060-6148  
City Area Code 804  
Local Phone Number 747-0136  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Shell Company false  
Amendment Flag false  
Document Period End Date Jun. 30, 2019  
Document Fiscal Year Focus 2019  
Document Fiscal Period Focus Q2  
Entity Registrant Name MARKEL CORP  
Entity Central Index Key 0001096343  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Entity Emerging Growth Company false  
Entity Small Business false  
Entity Common Stock, Shares Outstanding   13,822,820
Entity Tax Identification Number 54-1959284  
Trading Symbol MKL  
Security Exchange Name NYSE