v3.25.2
Segment Information - Operating Results (Detail) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Segment Reporting Information [Line Items]        
Net premiums earned $ 20,310 $ 17,209 $ 39,719 $ 33,358
Fees and other revenues 303 260 590 496
Total underwriting revenue 20,613 17,469 40,309 33,854
Losses (excluding catastrophe losses) 11,134 9,728 21,802 18,882
Catastrophe losses 707 1,269 1,166 1,616
Loss adjustment expenses 1,764 1,598 3,441 3,069
Losses and loss adjustment expenses 13,605 12,595 26,409 23,567
Distribution Expenses 2,637 2,112 5,271 3,946
Other Underwriting Expense, Adjusted 1,563 1,376 3,104 2,705
Total underwriting expenses 4,200 3,488 8,375 6,651
Pretax underwriting profit (loss) 2,808 1,386 5,525 3,636
Investment profit (loss) 1,249 551 1,844 1,319
Service businesses profit (loss) (6) (8) (12) (16)
Interest expense (69) (69) (139) (139)
Income before income taxes 3,982 1,860 7,218 4,800
Operating Segments | Personal Lines | Underwriting operations        
Segment Reporting Information [Line Items]        
Net premiums earned 17,544 14,545 34,254 28,136
Fees and other revenues 263 216 512 412
Total underwriting revenue 17,807 14,761 34,766 28,548
Losses (excluding catastrophe losses) 9,574 8,148 18,683 15,711
Catastrophe losses 688 1,243 1,142 1,581
Loss adjustment expenses 1,471 1,324 2,861 2,521
Losses and loss adjustment expenses 11,733 10,715 22,686 19,813
Distribution Expenses 2,328 1,828 4,676 3,388
Other Underwriting Expense, Adjusted 1,298 1,135 2,573 2,223
Total underwriting expenses 3,626 2,963 7,249 5,611
Pretax underwriting profit (loss) 2,448 1,083 4,831 3,124
Operating Segments | Commercial Lines | Underwriting operations        
Segment Reporting Information [Line Items]        
Net premiums earned 2,765 2,664 5,464 5,222
Fees and other revenues 40 44 78 84
Total underwriting revenue 2,805 2,708 5,542 5,306
Losses (excluding catastrophe losses) 1,561 1,581 3,120 3,174
Catastrophe losses 19 26 24 35
Loss adjustment expenses 292 274 579 548
Losses and loss adjustment expenses 1,872 1,881 3,723 3,757
Distribution Expenses 308 284 594 558
Other Underwriting Expense, Adjusted 261 239 523 478
Total underwriting expenses 569 523 1,117 1,036
Pretax underwriting profit (loss) 364 304 702 513
Operating Segments | Other Indemnity | Underwriting operations        
Segment Reporting Information [Line Items]        
Net premiums earned 1 0 1 0
Fees and other revenues 0 0 0 0
Total underwriting revenue 1 0 1 0
Losses (excluding catastrophe losses) (1) (1) (1) (3)
Catastrophe losses 0 0 0 0
Loss adjustment expenses 1 0 1 0
Losses and loss adjustment expenses 0 (1) 0 (3)
Distribution Expenses 1 0 1 0
Other Underwriting Expense, Adjusted 4 2 8 4
Total underwriting expenses 5 2 9 4
Pretax underwriting profit (loss) $ (4) $ (1) $ (8) $ (1)