v3.26.3
Segment Information (Details)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
USD ($)
Sep. 30, 2025
USD ($)
Sep. 30, 2026
USD ($)
segment
Sep. 30, 2025
USD ($)
Segment reporting information        
Number of reportable business segments | segment     3  
Premiums $ 11,103 $ 11,135 $ 32,461 $ 32,766
Net investment income 1,098 1,033 3,176 2,905
Fee income 123 127 370 370
Other revenues 122 148 407 383
Claims and claim adjustment expenses 6,487 6,594 18,791 21,389
Amortization of deferred acquisition costs 1,856 1,849 5,408 5,429
General and administrative expenses 1,582 1,572 4,688 4,576
Income tax expense 452 456 1,419 901
Net realized investment gains (losses) (34) 27 75 (28)
Total revenues 12,412 12,470 36,489 36,396
Core income (loss) 1,947 1,867 5,803 3,814
Net realized investment gains (losses), net of tax (30) 21 33 (22)
Net income 1,917 1,888 5,836 3,792
Reportable Segments [Member]        
Segment reporting information        
Premiums 11,103 11,135 32,461 32,766
Net investment income 1,098 1,033 3,176 2,905
Fee income 123 127 370 370
Other revenues 122 148 407 383
Total segment revenues 12,446 12,443 36,414 36,424
Claims and claim adjustment expenses 6,487 6,594 18,791 21,389
Amortization of deferred acquisition costs 1,856 1,849 5,408 5,429
General and administrative expenses 1,569 1,559 4,649 4,540
Income tax expense 483 477 1,459 982
Core income (loss) 2,051 1,964 6,107 4,084
Reportable Segments [Member] | Business Insurance [Member]        
Segment reporting information        
Premiums 5,862 5,700 16,906 16,710
Net investment income 766 727 2,236 2,045
Fee income 118 114 346 333
Other revenues 94 111 311 288
Total segment revenues 6,840 6,652 19,799 19,376
Claims and claim adjustment expenses 3,643 3,667 10,362 10,956
Amortization of deferred acquisition costs 1,001 973 2,884 2,834
General and administrative expenses 919 894 2,743 2,616
Income tax expense 241 211 737 567
Core income (loss) 1,036 907 3,073 2,403
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member]        
Segment reporting information        
Premiums 5,391 5,196 15,733 15,261
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Workers' compensation [Member]        
Segment reporting information        
Premiums 871 842 2,548 2,506
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Automobile [Member]        
Segment reporting information        
Premiums 1,092 1,011 3,169 2,921
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Commercial property [Member]        
Segment reporting information        
Premiums 909 942 2,726 2,839
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | General liability [Member]        
Segment reporting information        
Premiums 978 907 2,754 2,630
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Commercial multi-peril [Member]        
Segment reporting information        
Premiums 1,519 1,474 4,480 4,309
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Other [Member]        
Segment reporting information        
Premiums 22 20 56 56
Reportable Segments [Member] | Business Insurance [Member] | International [Member]        
Segment reporting information        
Premiums 471 504 1,173 1,449
Reportable Segments [Member] | Bond & Specialty Insurance [Member]        
Segment reporting information        
Premiums 1,103 1,042 3,177 3,058
Net investment income 127 116 353 325
Fee income 0 0 0 0
Other revenues 6 8 17 19
Total segment revenues 1,236 1,166 3,547 3,402
Claims and claim adjustment expenses 425 451 1,324 1,303
Amortization of deferred acquisition costs 215 197 613 579
General and administrative expenses 218 207 655 626
Income tax expense 69 61 158 180
Core income (loss) 309 250 797 714
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member]        
Segment reporting information        
Premiums 969 902 2,797 2,655
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member] | General liability [Member]        
Segment reporting information        
Premiums 473 463 1,391 1,374
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member] | Fidelity and surety [Member]        
Segment reporting information        
Premiums 435 378 1,226 1,103
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member] | Other [Member]        
Segment reporting information        
Premiums 61 61 180 178
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | International [Member]        
Segment reporting information        
Premiums 134 140 380 403
Reportable Segments [Member] | Personal Insurance [Member]        
Segment reporting information        
Premiums 4,138 4,393 12,378 12,998
Net investment income 205 190 587 535
Fee income 5 13 24 37
Other revenues 22 29 79 76
Total segment revenues 4,370 4,625 13,068 13,646
Claims and claim adjustment expenses 2,419 2,476 7,105 9,130
Amortization of deferred acquisition costs 640 679 1,911 2,016
General and administrative expenses 432 458 1,251 1,298
Income tax expense 173 205 564 235
Core income (loss) 706 807 2,237 967
Reportable Segments [Member] | Personal Insurance [Member] | Domestic [Member]        
Segment reporting information        
Premiums 4,138 4,226 12,378 12,494
Reportable Segments [Member] | Personal Insurance [Member] | Domestic [Member] | Automobile [Member]        
Segment reporting information        
Premiums 1,874 1,987 5,663 5,931
Reportable Segments [Member] | Personal Insurance [Member] | Domestic [Member] | Homeowners and Other [Member]        
Segment reporting information        
Premiums 2,264 2,239 6,715 6,563
Reportable Segments [Member] | Personal Insurance [Member] | International [Member]        
Segment reporting information        
Premiums 0 167 0 504
Other [Member]        
Segment reporting information        
Core income (loss) (104) (97) (304) (270)
After-tax interest expense $ 93 $ 88 $ 274 $ 244