v3.26.3
Segments of Operations - Revenues by segment and sub-segment (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Segment Reporting [Line Items]        
Net earned premiums $ 2,164 $ 2,013 $ 5,467 $ 5,240
Net investment income 356 205 764 562
Other income 29 30 87 84
Revenues before realized gains (losses) 2,618 2,318 6,504 6,093
Realized gains (losses) on securities (35) 12 (37) 17
Realized gain on subsidiaries 0 1 0 1
Total revenues 2,583 2,331 6,467 6,111
Investment income 362 211 783 581
Charleston Harbor Resort & Marina        
Segment Reporting [Line Items]        
Investment income 126 0 126 0
Operating segments | Property and casualty insurance        
Segment Reporting [Line Items]        
Net earned premiums 2,164 2,013 5,467 5,240
Net investment income 289 205 678 554
Other income 3 6 10 9
Revenues before realized gains (losses) 2,456 2,224 6,155 5,803
Operating segments | Property and casualty insurance | Property and transportation        
Segment Reporting [Line Items]        
Net earned premiums 1,026 935 2,142 2,011
Operating segments | Property and casualty insurance | Specialty casualty        
Segment Reporting [Line Items]        
Net earned premiums 831 810 2,444 2,403
Operating segments | Property and casualty insurance | Specialty financial        
Segment Reporting [Line Items]        
Net earned premiums 307 268 881 826
Operating segments | Other        
Segment Reporting [Line Items]        
Revenues before realized gains (losses) $ 162 $ 94 $ 349 $ 290