v3.26.1
Unpaid losses and loss expenses Unpaid losses and loss expenses (PPD table) (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development $ (283) $ (249) $ (569) $ (504)
North America Commercial P&C Insurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development (111) (106) (200) (220)
North America Personal P&C Insurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development (173) (121) (174) (121)
North American Agriculture Insurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development 0 0 (80) (33)
Overseas General Insurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development (146) (77) (277) (198)
Global Reinsurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development (11) (15) (11) (15)
Corporate Segment [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development 158 70 173 83
Short Tail [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development (393) (279) (715) (591)
Short Tail [Member] | North America Commercial P&C Insurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development (42) (31) (152) (193)
Short Tail [Member] | North America Personal P&C Insurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development (173) (121) (174) (121)
Short Tail [Member] | North American Agriculture Insurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development 0 0 (80) (33)
Short Tail [Member] | Overseas General Insurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development (157) (112) (288) (234)
Short Tail [Member] | Global Reinsurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development (21) (15) (21) (10)
Short Tail [Member] | Corporate Segment [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development 0 0 0 0
Long Tail [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development 110 30 146 87
Long Tail [Member] | North America Commercial P&C Insurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development (69) (75) (48) (27)
Long Tail [Member] | North America Personal P&C Insurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development 0 0 0 0
Long Tail [Member] | North American Agriculture Insurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development 0 0 0 0
Long Tail [Member] | Overseas General Insurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development 11 35 11 36
Long Tail [Member] | Global Reinsurance [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development 10 0 10 (5)
Long Tail [Member] | Corporate Segment [Member]        
Liability for Claims and Claims Adjustment Expense [Line Items]        
Net Prior Period Development $ 158 $ 70 $ 173 $ 83