Name:	mkl_AdjustmenttoLifeandAnnuityBenefits
Namespace Prefix:	mkl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Annuities included in life and annuity benefits in the consolidated balance sheet subject to discretionary withdrawal.

No definition available.

Name:	mkl_AnnuitiesSubjectToDiscretionaryWithdrawal
Namespace Prefix:	mkl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The cumulative adjustment to life and annuity benefits attributable to unrealized gains on the underlying investment portfolio.

No definition available.

Name:	mkl_CumulativeAdjustmentLifeandAnnuityBenefits
Namespace Prefix:	mkl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The largest life and annuity benefits reserve for a single contract.

No definition available.

Name:	mkl_LifeAndAnnuityBenefitsReserveSingleContractConcentration
Namespace Prefix:	mkl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Average interest rate for traditional life contracts used to calculate future benefits to be paid to or on behalf of policyholders and related expenses less the present value of future net premiums using assumptions such as estimates of expected investment yields, mortality, morbidity, terminations and expenses, applicable at the time the insurance contracts are made and costs of settling insured claims and costs incurred in the claims settlement process of traditional life.

No definition available.

Name:	mkl_TraditionalLifeInterestRateAverage
Namespace Prefix:	mkl_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- References

No definition available.