v3.25.2
Segments of Operations - Components of underwriting profit, including significant segment expenses by segment and sub-segment (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Segment Reporting Information [Line Items]        
Net earned premiums $ 1,647 $ 1,585 $ 3,227 $ 3,131
Losses and loss adjustment expenses 1,007 937 1,972 1,849
Commissions and other underwriting expenses 534 506 1,064 1,009
Operating segments | Property and Casualty Insurance        
Segment Reporting Information [Line Items]        
Net earned premiums 1,647 1,585 3,227 3,131
Losses and loss adjustment expenses 1,007 937 1,972 1,844
Commissions and other underwriting expenses 527 498 1,048 984
Property and casualty insurance underwriting profit 113 150 207 303
Operating segments | Property and transportation | Property and Casualty Insurance        
Segment Reporting Information [Line Items]        
Net earned premiums 576 552 1,076 1,072
Losses and loss adjustment expenses 387 351 698 657
Commissions and other underwriting expenses 162 161 314 315
Property and casualty insurance underwriting profit 27 40 64 100
Operating segments | Specialty casualty | Property and Casualty Insurance        
Segment Reporting Information [Line Items]        
Net earned premiums 799 791 1,593 1,574
Losses and loss adjustment expenses 516 483 1,052 985
Commissions and other underwriting expenses 234 222 472 442
Property and casualty insurance underwriting profit 49 86 69 147
Operating segments | Specialty financial | Property and Casualty Insurance        
Segment Reporting Information [Line Items]        
Net earned premiums 272 242 558 485
Losses and loss adjustment expenses 103 102 221 200
Commissions and other underwriting expenses 131 115 262 227
Property and casualty insurance underwriting profit 38 25 75 58
Operating segments | Other lines | Property and Casualty Insurance        
Segment Reporting Information [Line Items]        
Losses and loss adjustment expenses 1 1 1 2
Property and casualty insurance underwriting profit $ (1) $ (1) $ (1) $ (2)