v3.26.1
Segments of Operations - Revenues by segment and sub-segment (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Segment Reporting [Line Items]        
Net earned premiums $ 1,694 $ 1,647 $ 3,303 $ 3,227
Net investment income 221 184 408 357
Other income 29 27 58 54
Revenues before realized gains (losses) 2,014 1,922 3,886 3,775
Realized gains (losses) on securities 16 2 (2) 5
Total revenues 2,030 1,924 3,884 3,780
Operating segments | Property and casualty insurance        
Segment Reporting [Line Items]        
Net earned premiums 1,694 1,647 3,303 3,227
Net investment income 221 179 389 349
Other income 3 0 7 3
Revenues before realized gains (losses) 1,918 1,826 3,699 3,579
Operating segments | Property and casualty insurance | Property and transportation        
Segment Reporting [Line Items]        
Net earned premiums 590 576 1,116 1,076
Operating segments | Property and casualty insurance | Specialty casualty        
Segment Reporting [Line Items]        
Net earned premiums 814 799 1,613 1,593
Operating segments | Property and casualty insurance | Specialty financial        
Segment Reporting [Line Items]        
Net earned premiums 290 272 574 558
Operating segments | Other        
Segment Reporting [Line Items]        
Revenues before realized gains (losses) $ 96 $ 96 $ 187 $ 196