v3.25.3
Segment Information (Details)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2025
USD ($)
Sep. 30, 2024
USD ($)
Sep. 30, 2025
USD ($)
segment
Sep. 30, 2024
USD ($)
Segment reporting information        
Number of reportable business segments | segment     3  
Premiums $ 11,135 $ 10,704 $ 32,766 $ 31,073
Net investment income 1,033 904 2,905 2,635
Fee income 127 121 370 345
Other revenues 148 120 383 337
Claims and claim adjustment expenses 6,594 6,996 21,389 21,025
Amortization of deferred acquisition costs 1,849 1,790 5,429 5,166
General and administrative expenses 1,572 1,460 4,576 4,344
Income tax expense 456 300 901 669
Net realized investment gains (losses) 27 55 (28) 25
Total revenues 12,470 11,904 36,396 34,415
Core income (loss) 1,867 1,218 3,814 2,899
Net realized investment gains (losses), net of tax 21 42 (22) 18
Net income 1,888 1,260 3,792 2,917
Reportable Segments [Member]        
Segment reporting information        
Premiums 11,135 10,704 32,766 31,073
Net investment income 1,033 904 2,905 2,635
Fee income 127 121 370 345
Other revenues 148 120 383 337
Total segment revenues 12,443 11,849 36,424 34,390
Claims and claim adjustment expenses 6,594 6,996 21,389 21,025
Amortization of deferred acquisition costs 1,849 1,790 5,429 5,166
General and administrative expenses 1,559 1,449 4,540 4,313
Income tax expense 477 310 982 730
Core income (loss) 1,964 1,304 4,084 3,156
Reportable Segments [Member] | Business Insurance [Member]        
Segment reporting information        
Premiums 5,700 5,474 16,710 15,802
Net investment income 727 642 2,045 1,883
Fee income 114 109 333 315
Other revenues 111 89 288 243
Total segment revenues 6,652 6,314 19,376 18,243
Claims and claim adjustment expenses 3,667 3,698 10,956 10,500
Amortization of deferred acquisition costs 973 930 2,834 2,655
General and administrative expenses 894 826 2,616 2,479
Income tax expense 211 162 567 491
Core income (loss) 907 698 2,403 2,118
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member]        
Segment reporting information        
Premiums 5,196 4,954 15,261 14,437
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Workers' compensation [Member]        
Segment reporting information        
Premiums 842 858 2,506 2,602
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Automobile [Member]        
Segment reporting information        
Premiums 1,011 915 2,921 2,649
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Commercial property [Member]        
Segment reporting information        
Premiums 942 915 2,839 2,682
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | General liability [Member]        
Segment reporting information        
Premiums 907 871 2,630 2,563
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Commercial multi-peril [Member]        
Segment reporting information        
Premiums 1,474 1,374 4,309 3,890
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Other [Member]        
Segment reporting information        
Premiums 20 21 56 51
Reportable Segments [Member] | Business Insurance [Member] | International [Member]        
Segment reporting information        
Premiums 504 520 1,449 1,365
Reportable Segments [Member] | Bond & Specialty Insurance [Member]        
Segment reporting information        
Premiums 1,042 1,009 3,058 2,942
Net investment income 116 101 325 285
Fee income 0 0 0 0
Other revenues 8 7 19 22
Total segment revenues 1,166 1,117 3,402 3,249
Claims and claim adjustment expenses 451 441 1,303 1,342
Amortization of deferred acquisition costs 197 194 579 559
General and administrative expenses 207 203 626 615
Income tax expense 61 57 180 146
Core income (loss) 250 222 714 587
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member]        
Segment reporting information        
Premiums 902 871 2,655 2,538
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member] | General liability [Member]        
Segment reporting information        
Premiums 463 454 1,374 1,317
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member] | Fidelity and surety [Member]        
Segment reporting information        
Premiums 378 359 1,103 1,049
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member] | Other [Member]        
Segment reporting information        
Premiums 61 58 178 172
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | International [Member]        
Segment reporting information        
Premiums 140 138 403 404
Reportable Segments [Member] | Personal Insurance [Member]        
Segment reporting information        
Premiums 4,393 4,221 12,998 12,329
Net investment income 190 161 535 467
Fee income 13 12 37 30
Other revenues 29 24 76 72
Total segment revenues 4,625 4,418 13,646 12,898
Claims and claim adjustment expenses 2,476 2,857 9,130 9,183
Amortization of deferred acquisition costs 679 666 2,016 1,952
General and administrative expenses 458 420 1,298 1,219
Income tax expense 205 91 235 93
Core income (loss) 807 384 967 451
Reportable Segments [Member] | Personal Insurance [Member] | Domestic [Member]        
Segment reporting information        
Premiums 4,226 4,056 12,494 11,835
Reportable Segments [Member] | Personal Insurance [Member] | Domestic [Member] | Automobile [Member]        
Segment reporting information        
Premiums 1,987 1,973 5,931 5,766
Reportable Segments [Member] | Personal Insurance [Member] | Domestic [Member] | Homeowners and Other [Member]        
Segment reporting information        
Premiums 2,239 2,083 6,563 6,069
Reportable Segments [Member] | Personal Insurance [Member] | International [Member]        
Segment reporting information        
Premiums 167 165 504 494
Other [Member]        
Segment reporting information        
Core income (loss) (97) (86) (270) (257)
After-tax interest expense $ 88 $ 77 $ 244 $ 232