v3.26.1
Segment Information (Details)
$ in Millions
 3 Months Ended
Mar. 31, 2026
USD ($)
segment
Mar. 31, 2025
USD ($)
Segment reporting information    
Number of reportable business segments | segment 3  
Premiums $ 10,605 $ 10,710
Net investment income 1,008 930
Fee income 121 119
Other revenues 141 112
Claims and claim adjustment expenses 6,382 8,006
Amortization of deferred acquisition costs 1,766 1,778
General and administrative expenses 1,541 1,459
Income tax expense (benefit) 408 73
Net realized investment gains (losses) 49 (61)
Total revenues 11,924 11,810
Core income (loss) 1,696 443
Net realized investment gains (losses), net of tax 15 (48)
Net income 1,711 395
Reportable Segments [Member]    
Segment reporting information    
Premiums 10,605 10,710
Net investment income 1,008 930
Fee income 121 119
Other revenues 141 112
Total segment revenues 11,875 11,871
Claims and claim adjustment expenses 6,382 8,006
Amortization of deferred acquisition costs 1,766 1,778
General and administrative expenses 1,528 1,448
Income tax expense (benefit) 402 110
Core income (loss) 1,797 529
Reportable Segments [Member] | Business Insurance [Member]    
Segment reporting information    
Premiums 5,493 5,465
Net investment income 708 656
Fee income 111 108
Other revenues 104 82
Total segment revenues 6,416 6,311
Claims and claim adjustment expenses 3,531 3,705
Amortization of deferred acquisition costs 938 917
General and administrative expenses 912 847
Income tax expense (benefit) 196 159
Core income (loss) 839 683
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member]    
Segment reporting information    
Premiums 5,134 4,982
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Workers' compensation [Member]    
Segment reporting information    
Premiums 831 823
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Automobile [Member]    
Segment reporting information    
Premiums 1,024 942
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Commercial property [Member]    
Segment reporting information    
Premiums 907 937
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | General liability [Member]    
Segment reporting information    
Premiums 890 861
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Commercial multi-peril [Member]    
Segment reporting information    
Premiums 1,465 1,400
Reportable Segments [Member] | Business Insurance [Member] | Domestic [Member] | Other [Member]    
Segment reporting information    
Premiums 17 19
Reportable Segments [Member] | Business Insurance [Member] | International [Member]    
Segment reporting information    
Premiums 359 483
Reportable Segments [Member] | Bond & Specialty Insurance [Member]    
Segment reporting information    
Premiums 1,018 995
Net investment income 113 102
Fee income 0 0
Other revenues 5 6
Total segment revenues 1,136 1,103
Claims and claim adjustment expenses 441 434
Amortization of deferred acquisition costs 194 187
General and administrative expenses 219 205
Income tax expense (benefit) 28 57
Core income (loss) 254 220
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member]    
Segment reporting information    
Premiums 899 868
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member] | General liability [Member]    
Segment reporting information    
Premiums 455 452
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member] | Fidelity and surety [Member]    
Segment reporting information    
Premiums 385 358
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | Domestic [Member] | Other [Member]    
Segment reporting information    
Premiums 59 58
Reportable Segments [Member] | Bond & Specialty Insurance [Member] | International [Member]    
Segment reporting information    
Premiums 119 127
Reportable Segments [Member] | Personal Insurance [Member]    
Segment reporting information    
Premiums 4,094 4,250
Net investment income 187 172
Fee income 10 11
Other revenues 32 24
Total segment revenues 4,323 4,457
Claims and claim adjustment expenses 2,410 3,867
Amortization of deferred acquisition costs 634 674
General and administrative expenses 397 396
Income tax expense (benefit) 178 (106)
Core income (loss) 704 (374)
Reportable Segments [Member] | Personal Insurance [Member] | Domestic [Member]    
Segment reporting information    
Premiums 4,094 4,085
Reportable Segments [Member] | Personal Insurance [Member] | Domestic [Member] | Automobile [Member]    
Segment reporting information    
Premiums 1,892 1,964
Reportable Segments [Member] | Personal Insurance [Member] | Domestic [Member] | Homeowners and Other [Member]    
Segment reporting information    
Premiums 2,202 2,121
Reportable Segments [Member] | Personal Insurance [Member] | International [Member]    
Segment reporting information    
Premiums 0 165
Other [Member]    
Segment reporting information    
Core income (loss) (101) (86)
After-tax interest expense $ 92 $ 78