v3.26.3
Segment Information - Operating Results (Detail) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Segment Reporting [Line Items]        
Net premiums earned $ 21,869 $ 20,849 $ 64,410 $ 60,568
Fees and other revenues 311 306 913 896
Total underwriting revenue 22,180 21,155 65,323 61,464
Losses (excluding catastrophe losses) 12,584 11,377 36,158 33,179
Catastrophe losses 388 219 1,429 1,385
Loss adjustment expenses 1,932 1,849 5,716 5,290
Losses and loss adjustment expenses 14,904 13,445 43,303 39,854
Distribution expenses 3,092 2,821 8,913 8,092
Other underwriting expenses 1,711 2,699 5,052 5,803
Total underwriting expenses 4,803 5,520 13,965 13,895
Pretax underwriting profit (loss) 2,473 2,190 8,055 7,715
Investment profit (loss) 855 1,209 3,217 3,053
Service businesses profit (loss) (5) (6) (16) (18)
Interest expense (87) (70) (245) (209)
Income before income taxes 3,236 3,323 11,011 10,541
Policyholder credit expense 0 950 0 950
FLORIDA        
Segment Reporting [Line Items]        
Policyholder credit expense   950   950
Operating Segments | Personal Lines | Underwriting operations        
Segment Reporting [Line Items]        
Net premiums earned 19,060 18,089 56,324 52,343
Fees and other revenues 291 272 855 784
Total underwriting revenue 19,351 18,361 57,179 53,127
Losses (excluding catastrophe losses) 10,888 9,801 31,608 28,484
Catastrophe losses 373 207 1,395 1,349
Loss adjustment expenses 1,605 1,554 4,798 4,415
Losses and loss adjustment expenses 12,866 11,562 37,801 34,248
Distribution expenses 2,749 2,507 7,949 7,183
Other underwriting expenses 1,455 2,394 4,227 4,967
Total underwriting expenses 4,204 4,901 12,176 12,150
Pretax underwriting profit (loss) 2,281 1,898 7,202 6,729
Operating Segments | Commercial Lines | Underwriting operations        
Segment Reporting [Line Items]        
Net premiums earned 2,807 2,760 8,081 8,224
Fees and other revenues 20 34 58 112
Total underwriting revenue 2,827 2,794 8,139 8,336
Losses (excluding catastrophe losses) 1,689 1,575 4,536 4,695
Catastrophe losses 15 12 34 36
Loss adjustment expenses 327 296 918 875
Losses and loss adjustment expenses 2,031 1,883 5,488 5,606
Distribution expenses 340 313 956 907
Other underwriting expenses 249 300 807 823
Total underwriting expenses 589 613 1,763 1,730
Pretax underwriting profit (loss) 207 298 888 1,000
Operating Segments | Other Indemnity | Underwriting operations        
Segment Reporting [Line Items]        
Net premiums earned 2 0 5 1
Fees and other revenues 0 0 0 0
Total underwriting revenue 2 0 5 1
Losses (excluding catastrophe losses) 7 1 14 0
Catastrophe losses 0 0 0 0
Loss adjustment expenses 0 (1) 0 0
Losses and loss adjustment expenses 7 0 14 0
Distribution expenses 3 1 8 2
Other underwriting expenses 7 5 18 13
Total underwriting expenses 10 6 26 15
Pretax underwriting profit (loss) $ (15) $ (6) $ (35) $ (14)