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Unpaid losses and loss expenses Unpaid losses and loss expenses (PPD table) (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2024 | Mar. 31, 2023
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | $ (207) | $ (196)
North America Commercial P&C Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (48) | (72)
North America Personal P&C Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (52) | 17
North American Agriculture Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (28) | 0
Overseas General Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (89) | (143)
Global Reinsurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 1 | (8)
Corporate Segment [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 9 | 10
Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (311) | (215)
Short Tail [Member] | North America Commercial P&C Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (144) | (81)
Short Tail [Member] | North America Personal P&C Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (52) | 17
Short Tail [Member] | North American Agriculture Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (28) | 0
Short Tail [Member] | Overseas General Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (88) | (143)
Short Tail [Member] | Global Reinsurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 1 | (8)
Short Tail [Member] | Corporate Segment [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 0 | 0
Long Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 104 | 19
Long Tail [Member] | North America Commercial P&C Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 96 | 9
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
Long Tail [Member] | North American Agriculture Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 0 | 0
Long Tail [Member] | Overseas General Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (1) | 0
Long Tail [Member] | Global Reinsurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 0 | 0
Long Tail [Member] | Corporate Segment [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | $ 9 | $ 10

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