In a well‐designed enterprise risk management (ERM) program, the firm integrates risk management into the strategic planning process, addressing strategic, financial, operational, and hazard risks under a single overarching process. This is particularly important to large financial firms, such as property and casualty (P&C) insurers, which face a diverse set of risks. Using a sample of P&C insurers with S&P ERM quality ratings from 2006 to 2013, we find that the quality of a firm's ERM is a significant determinant of P&C insurer performance and that, for firms with high‐quality ERM programs, product line diversification has a significant positive effect on performance.