| Cover Page Statement | Nov. 16, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Document Period End Date | Nov. 16, 2021 |
| Entity Registrant Name | Markel Corporation |
| Entity Incorporation, State or Country Code | VA |
| Entity File Number | 001-15811 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, no par value |
| Trading Symbol | MKL |
| Security Exchange Name | NYSE |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0001096343 |
