v3.26.1
Segment Information (Details)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
USD ($)
Jun. 30, 2025
USD ($)
Jun. 30, 2026
USD ($)
segment
Jun. 30, 2025
USD ($)
Segment reporting information        
Number of reportable business segments | segment     3  
Premiums $ 10,753 $ 10,921 $ 21,358 $ 21,631
Net investment income 1,070 942 2,078 1,872
Fee income 126 124 247 243
Other revenues 144 123 285 235
Claims and claim adjustment expenses 5,922 6,789 12,304 14,795
Amortization of deferred acquisition costs 1,786 1,802 3,552 3,580
General and administrative expenses 1,565 1,545 3,106 3,004
Income tax expense 559 372 967 445
Net realized investment gains (losses) 60 6 109 (55)
Total revenues 12,153 12,116 24,077 23,926
Core income (loss) 2,160 1,504 3,856 1,947
Net realized investment gains (losses), net of tax 48 5 63 (43)
Net income 2,208 1,509 3,919 1,904
Reportable Segments [Member]        
Segment reporting information        
Premiums 10,753 10,921 21,358 21,631
Net investment income 1,070 942 2,078 1,872
Fee income 126 124 247 243
Other revenues 144 123 285 235
Total segment revenues 12,093 12,110 23,968 23,981
Claims and claim adjustment expenses 5,922 6,789 12,304 14,795
Amortization of deferred acquisition costs 1,786 1,802 3,552 3,580
General and administrative expenses 1,552 1,533 3,080 2,981
Income tax expense 574 395 976 505
Core income (loss) 2,259 1,591 4,056 2,120
Reportable Segments [Member] | Business Insurance [Member]        
Segment reporting information        
Premiums 5,551 5,545 11,044 11,010
Net investment income 762 662 1,470 1,318
Fee income 117 111 228 219
Other revenues 113 95 217 177
Total segment revenues 6,543 6,413 12,959 12,724
Claims and claim adjustment expenses 3,188 3,584 6,719 7,289
Amortization of deferred acquisition costs 945 944 1,883 1,861
General and administrative expenses 912 875 1,824 1,722
Income tax expense 300 197 496 356
Core income (loss) 1,198 813 2,037 1,496
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member]        
Segment reporting information        
Premiums 5,208 5,083 10,342 10,065
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Workers' compensation [Member]        
Segment reporting information        
Premiums 846 841 1,677 1,664
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Automobile [Member]        
Segment reporting information        
Premiums 1,053 968 2,077 1,910
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Commercial property [Member]        
Segment reporting information        
Premiums 910 960 1,817 1,897
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | General liability [Member]        
Segment reporting information        
Premiums 886 862 1,776 1,723
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Commercial multi-peril [Member]        
Segment reporting information        
Premiums 1,496 1,435 2,961 2,835
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Other [Member]        
Segment reporting information        
Premiums 17 17 34 36
Reportable Segments [Member] | Business Insurance [Member] | International [Member]        
Segment reporting information        
Premiums 343 462 702 945
Reportable Segments [Member] | Bond & Specialty Insurance [Member]        
Segment reporting information        
Premiums 1,056 1,021 2,074 2,016
Net investment income 113 107 226 209
Fee income 0 0 0 0
Other revenues 6 5 11 11
Total segment revenues 1,175 1,133 2,311 2,236
Claims and claim adjustment expenses 458 418 899 852
Amortization of deferred acquisition costs 204 195 398 382
General and administrative expenses 218 214 437 419
Income tax expense 61 62 89 119
Core income (loss) 234 244 488 464
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member]        
Segment reporting information        
Premiums 929 885 1,828 1,753
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member] | General liability [Member]        
Segment reporting information        
Premiums 463 459 918 911
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member] | Fidelity and surety [Member]        
Segment reporting information        
Premiums 406 367 791 725
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member] | Other [Member]        
Segment reporting information        
Premiums 60 59 119 117
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | International [Member]        
Segment reporting information        
Premiums 127 136 246 263
Reportable Segments [Member] | Personal Insurance [Member]        
Segment reporting information        
Premiums 4,146 4,355 8,240 8,605
Net investment income 195 173 382 345
Fee income 9 13 19 24
Other revenues 25 23 57 47
Total segment revenues 4,375 4,564 8,698 9,021
Claims and claim adjustment expenses 2,276 2,787 4,686 6,654
Amortization of deferred acquisition costs 637 663 1,271 1,337
General and administrative expenses 422 444 819 840
Income tax expense 213 136 391 30
Core income (loss) 827 534 1,531 160
Reportable Segments [Member] | Personal Insurance [Member] | Domestic [Member]        
Segment reporting information        
Premiums 4,146 4,183 8,240 8,268
Reportable Segments [Member] | Personal Insurance [Member] | Domestic [Member] | Automobile [Member]        
Segment reporting information        
Premiums 1,897 1,980 3,789 3,944
Reportable Segments [Member] | Personal Insurance [Member] | Domestic [Member] | Homeowners and Other [Member]        
Segment reporting information        
Premiums 2,249 2,203 4,451 4,324
Reportable Segments [Member] | Personal Insurance [Member] | International [Member]        
Segment reporting information        
Premiums 0 172 0 337
Other [Member]        
Segment reporting information        
Core income (loss) (99) (87) (200) (173)
After-tax interest expense $ 89 $ 78 $ 181 $ 156