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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, 2022 | Mar. 31, 2021
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | $ (240) | $ (192)
North America Commercial P&C Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (108) | (127)
North America Personal P&C Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (51) | (40)
North American Agriculture Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (26) | (2)
Overseas General Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (60) | (25)
Global Reinsurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (3) | (7)
Corporate Segment [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 8 | 9
Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (228) | (155)
Short Tail [Member] | North America Commercial P&C Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (88) | (81)
Short Tail [Member] | North America Personal P&C Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (51) | (40)
Short Tail [Member] | North American Agriculture Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (26) | (2)
Short Tail [Member] | Overseas General Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (60) | (25)
Short Tail [Member] | Global Reinsurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (3) | (7)
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 | (12) | (37)
Long Tail [Member] | North America Commercial P&C Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (20) | (46)
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 | 0 | 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 | $ 8 | $ 9

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