Subsequent Events	9 Months Ended
Sep. 30, 2026
Subsequent Events [Abstract]
Subsequent Events	Subsequent Event On October 27, 2026, Markel Insurance entered into an adverse development cover reinsurance agreement with Cavello Bay Reinsurance Limited, a wholly-owned subsidiary of Enstar Group Limited (Enstar), covering a portfolio that includes the run-off Global Reinsurance business and certain exited lines within its insurance operations. The transaction is subject to regulatory approvals and other customary conditions and is expected to close in the fourth quarter of 2026. The reinsurance agreement is effective as of April 1, 2026 and includes subject reserves of $4.8 billion. Markel Insurance will retain the first $2.6 billion of reserves and retrocede the next $2.3 billion to Enstar in exchange for a corresponding transfer of assets. The agreement also provides adverse loss development coverage of $1.2 billion above the $4.8 billion of subject reserves in exchange for payment of a risk premium of $120 million. Subject reserves include 2025 and prior underwriting years of business written within the Global Reinsurance division and the exited risk-managed professional liability, architects and engineers, and certain other run-off product lines within the U.S. Wholesale and Specialty and Programs and Solutions divisions. Markel Insurance will maintain claims control for the covered reserves subject to certain administrative rights of Enstar.

Subsequent Events

9 Months Ended

Sep. 30, 2026

Subsequent Event

On October 27, 2026, Markel Insurance entered into an adverse development cover reinsurance agreement with Cavello Bay Reinsurance Limited, a wholly-owned subsidiary of Enstar Group Limited (Enstar), covering a portfolio that includes the run-off Global Reinsurance business and certain exited lines within its insurance operations. The transaction is subject to regulatory approvals and other customary conditions and is expected to close in the fourth quarter of 2026.

The reinsurance agreement is effective as of April 1, 2026 and includes subject reserves of $4.8 billion. Markel Insurance will retain the first $2.6 billion of reserves and retrocede the next $2.3 billion to Enstar in exchange for a corresponding transfer of assets. The agreement also provides adverse loss development coverage of $1.2 billion above the $4.8 billion of subject reserves in exchange for payment of a risk premium of $120 million.

Subject reserves include 2025 and prior underwriting years of business written within the Global Reinsurance division and the exited risk-managed professional liability, architects and engineers, and certain other run-off product lines within the U.S. Wholesale and Specialty and Programs and Solutions divisions. Markel Insurance will maintain claims control for the covered reserves subject to certain administrative rights of Enstar.