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Unpaid losses and loss expenses Unpaid losses and loss expenses (Narrative) (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)
Long Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (12) | (37)
Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (228) | (155)
North America Commercial P&C Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (108) | (127)
North America Commercial P&C Insurance [Member] | Long Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (20) | (46)
North America Commercial P&C Insurance [Member] | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (88) | (81)
North America Commercial P&C Insurance [Member] | Accident years 2018 - 2019 [Member] | Surety Product Line [Member] | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development |  | (49)
North America Commercial P&C Insurance [Member] | Short-Duration Insurance Contract, Accident Year 2020 | Surety Product Line [Member] | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (38) |
North America Commercial P&C Insurance [Member] | Short-Duration Insurance Contract, Accident Year 2020 | Property and Inland Marine [Member] | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development |  | (25)
North America Commercial P&C Insurance [Member] | Accident Years 2019 - 2020 | First Party Cyber risk [Member] | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development |  | 41
North America Commercial P&C Insurance [Member] | Accident Years 2019 - 2020 | Accident and Health Insurance Product Line [Member] | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development |  | (48)
North America Commercial P&C Insurance [Member] | Accident years 2017 and prior | Environmental lines [Member] | Long Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development |  | (35)
North America Commercial P&C Insurance [Member] | Accident years 2017 and prior | Workers' Compensation Insurance [Member] | Long Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (38) |
North America Commercial P&C Insurance [Member] | Accident years 2019 and prior [Member] | Commercial Excess and Umbrella [Member] | Long Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 60 |
North America Commercial P&C Insurance [Member] | Accident years 2020 and 2021 [Member] | Accident and Health Insurance Product Line [Member] | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (76) |
North America Commercial P&C Insurance [Member] | Accident years 2020 and 2021 [Member] | Property and Casualty, Personal Insurance [Member] | Long Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (38) |
North America Commercial P&C Insurance [Member] | Short-Duration Insurance Contract, Accident Year 2021 [Member] | Property, Liability and Casualty Insurance Product Line | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 21 |
North America Commercial P&C Insurance [Member] | Accident years 2016 and 2017 | Professional Malpractice Liability Insurance [Member] | Long Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development |  | (51)
North America Commercial P&C Insurance [Member] | Accident years 2015 to 2019 [Member] | Commercial Excess and Umbrella [Member] | Long Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development |  | 57
North America Agricultural Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (26) | (2)
North America Agricultural Insurance [Member] | Long Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 0 | 0
North America Agricultural Insurance [Member] | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (26) | (2)
North America Agricultural Insurance [Member] | Short-Duration Insurance Contract, Accident Year 2021 [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (26) |
Corporate Segment [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 8 | 9
Corporate Segment [Member] | Long Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 8 | 9
Corporate Segment [Member] | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 0 | 0
Overseas General Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (60) | (25)
Overseas General Insurance [Member] | Long Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 0 | 0
Overseas General Insurance [Member] | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (60) | (25)
Overseas General Insurance [Member] | Short-Duration Insurance Contract, Accident Year 2020 |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development |  | (25)
Overseas General Insurance [Member] | Accident years 2020 and 2021 [Member] | Accident and Health Insurance Product Line [Member] | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (22) |
Overseas General Insurance [Member] | Accident years 2020 and 2021 [Member] | Property, Liability and Casualty Insurance Product Line | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (24) |
North America Personal P&C Insurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (51) | (40)
North America Personal P&C Insurance [Member] | Long Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 0 | 0
North America Personal P&C Insurance [Member] | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (51) | (40)
North America Personal P&C Insurance [Member] | Short-Duration Insurance Contract, Accident Year 2020 |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development |  | (40)
North America Personal P&C Insurance [Member] | Short-Duration Insurance Contract, Accident Year 2021 [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (51) |
Global Reinsurance [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | (3) | (7)
Global Reinsurance [Member] | Long Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | 0 | 0
Global Reinsurance [Member] | Short Tail [Member] |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |
Net Prior Period Development | $ (3) | $ (7)

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