v3.26.1
Segment Information - Underwriting Margins and Combined Ratios for our Underwriting Operations (Detail) - Underwriting operations
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Segment Reporting [Line Items]        
Under- writing Margin 12.70% 13.80% 13.10% 13.90%
Combined Ratio 87.30% 86.20% 86.90% 86.10%
Operating Segments | Personal Lines        
Segment Reporting [Line Items]        
Under- writing Margin 12.40% 14.00% 13.20% 14.10%
Combined Ratio 87.60% 86.00% 86.80% 85.90%
Operating Segments | Commercial Lines        
Segment Reporting [Line Items]        
Under- writing Margin 14.70% 13.20% 12.90% 12.90%
Combined Ratio 85.30% 86.80% 87.10% 87.10%