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Unpaid losses and loss expenses Unpaid losses and loss expenses (PPD table) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2025 | Sep. 30, 2024
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | $ (361) | $ (244) | $ (865) | $ (643)
North America Commercial P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (26) | (39) | (246) | (231)
North America Personal P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (282) | (189) | (403) | (305)
North American Agriculture Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (30) | (6) | (63) | (34)
Overseas General Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (84) | (60) | (282) | (210)
Global Reinsurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 0 | (5) | (15) | (20)
Corporate Segment [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 61 | 55 | 144 | 157
Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (460) | (358) | (1,051) | (853)
Short Tail [Member] | North America Commercial P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (130) | (164) | (323) | (310)
Short Tail [Member] | North America Personal P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (282) | (189) | (403) | (305)
Short Tail [Member] | North American Agriculture Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (30) | (6) | (63) | (34)
Short Tail [Member] | Overseas General Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (18) | 1 | (252) | (184)
Short Tail [Member] | Global Reinsurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 0 | 0 | (10) | (20)
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 | 99 | 114 | 186 | 210
Long Tail [Member] | North America Commercial P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 104 | 125 | 77 | 79
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 | (66) | (61) | (30) | (26)
Long Tail [Member] | Global Reinsurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 0 | (5) | (5) | 0
Long Tail [Member] | Corporate Segment [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | $ 61 | $ 55 | $ 144 | $ 157

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