Document And Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 04, 2020	Jun. 30, 2019
Cover page.
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Entity File Number	001-15811
Entity Registrant Name	MARKEL CORPORATION
Entity Incorporation, State or Country Code	VA
Entity Tax Identification Number	54-1959284
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
Title of 12(b) Security	Common Stock, no par value
Trading Symbol	MKL
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 14,711,000,000
Entity Common Stock, Shares Outstanding		13,782,159
Document Annual Report	true
Document Transition Report	false
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Central Index Key	0001096343
Current Fiscal Year End Date	--12-31