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Unpaid losses and loss expenses Unpaid losses and loss expenses (Narrative) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | $ (146) | $ (167) | $ (189) | $ (559)
Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (278) | (252) | (197) | (514)
Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 132 | 85 | 8 | (45)
North America Commercial P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (200) | (109) | (451) | (425)
North America Commercial P&C Insurance [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (255) | (197) | (439) | (468)
North America Commercial P&C Insurance [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 55 | 88 | (12) | 43
North America Commercial P&C Insurance [Member] | Professional Malpractice Liability Insurance [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | (53)
North America Commercial P&C Insurance [Member] | Commercial Excess and Umbrella [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (47) |  |  | (63)
North America Commercial P&C Insurance [Member] | Workers' Compensation Insurance [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (155) |  | (337) | (294)
North America Commercial P&C Insurance [Member] | Other [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | 5 |
North America Commercial P&C Insurance [Member] | Multi-Line [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 26 | 34 |  |
North America Commercial P&C Insurance [Member] | Property Insurance [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 35 |  |  |
North America Commercial P&C Insurance [Member] | Property and Inland Marine [Member] | Short Tail [Member] | Other [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 116 |  |
North America Commercial P&C Insurance [Member] | Property and Inland Marine [Member] | Short Tail [Member] | Catastrophe [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (27) |  |
North America Commercial P&C Insurance [Member] | Accident Year 2013 and prior [Member] | Commercial Excess and Umbrella [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (32) |  |
North America Commercial P&C Insurance [Member] | Accident years 2014 - 2018 [Member] | Auto Liability [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | 31
North America Commercial P&C Insurance [Member] | Accident year 2015 and prior [Member] | Workers' Compensation Insurance [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (94) |  |
North America Commercial P&C Insurance [Member] | Accident year 2015 and prior [Member] | Multi-Line [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (36) |  | (36)
North America Commercial P&C Insurance [Member] | Accident year 2015 and prior [Member] | Foreign Casualty Line [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (39) |  | (39)
North America Commercial P&C Insurance [Member] | Accident years 2015 to 2019 [Member] | Auto Liability [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | 75 |
North America Commercial P&C Insurance [Member] | Accident years 2016 and prior [Member] | Professional Malpractice Liability Insurance [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | (66) |
North America Commercial P&C Insurance [Member] | Accident years 2016 and prior [Member] | Environmental lines [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | (43) |
North America Commercial P&C Insurance [Member] | Accident years 2016 and prior [Member] | General Liability [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 29 |  |  |
North America Commercial P&C Insurance [Member] | Accident years 2016 and prior [Member] | Multi-Line [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (41) |  | (41) |
North America Commercial P&C Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Foreign Casualty Line [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (40) |  | (40) |
North America Commercial P&C Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2017 [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] | Accident year 2017 and prior [Member] | Property and Inland Marine [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] | Accident year 2017 - 2018 [Member] | Property and Inland Marine [Member] | Short Tail [Member] | Catastrophe [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (41) |  |
North America Commercial P&C Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2018 [Member] | Surety Product Line [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | (31) |
North America Commercial P&C Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2018 [Member] | Workers' Compensation Insurance [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | 61
North America Commercial P&C Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2018 [Member] | Property and Inland Marine [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 154 |  |
North America Commercial P&C Insurance [Member] | Accident years 2018 - 2019 [Member] | Accident and Health Insurance Product Line [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | (37) |
North America Commercial P&C Insurance [Member] | Short-Duration Insurance Contract, Accident Year 2019 [Member] | Workers' Compensation Insurance [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | (62) |
North America Commercial P&C Insurance [Member] | Short-Duration Insurance Contract, Accident Year 2019 [Member] | Marine [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 21 |  |  |
North America Agricultural Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 18 | 18 | 4 | (43)
North America Agricultural Insurance [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 0 | 0 | 0 | 0
North America Agricultural Insurance [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 18 | 18 | 4 | (43)
Corporate Segment [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 54 | 36 | 339 | 79
Corporate Segment [Member] | Environmental Issue [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 35 | 27 |  |
Corporate Segment [Member] | Discontinued Operations [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | 28
Corporate Segment [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 54 | 36 | 339 | 79
Corporate Segment [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 0 | 0 | 0 | 0
Corporate Segment [Member] | Other [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | 254 |
Overseas General Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (60) | (25) | (100) | (49)
Overseas General Insurance [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (71) | (66) | (72) | (66)
Overseas General Insurance [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 11 | 41 | (28) | 17
Overseas General Insurance [Member] | Casualty lines [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (94) | (101) |  |
Overseas General Insurance [Member] | Financial [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 57 | 50 |  |
Overseas General Insurance [Member] | Accident year 2015 and prior [Member] | Casualty lines [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (123) |  |
Overseas General Insurance [Member] | Accident year 2015 and prior [Member] | Financial [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (68) | (75) |  |
Overseas General Insurance [Member] | Accident years 2016 and prior [Member] | Casualty lines [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (143) |  |  |
Overseas General Insurance [Member] | Accident Year 2016 through 2018 [Member] | Casualty lines [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 22 |  |
Overseas General Insurance [Member] | Accident Year 2016 through 2018 [Member] | Financial [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 125 |  |
Overseas General Insurance [Member] | Accident Year 2016 - 2019 [Member] | Financial [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 125 |  |  |
Overseas General Insurance [Member] | Accident year 2017 - 2018 [Member] | Surety Product Line [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 27 |  |
Overseas General Insurance [Member] | Accident year 2017 - 2018 [Member] | Marine [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | (22) |
Overseas General Insurance [Member] | Accident Year 2017 to 2019 [Member] | Casualty lines [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 49 |  |  |
Overseas General Insurance [Member] | Accident years 2018 - 2019 [Member] | Political Risk [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (22) |  |  |
North America Personal P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 48 | (62) | 48 | (88)
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 | 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 | 48 | (62) | 48 | (88)
North America Personal P&C Insurance [Member] | Personal lines [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (22) |  | (22) |
North America Personal P&C Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2016 [Member] | Personal lines [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (26) |  | (26)
North America Personal P&C Insurance [Member] | Accident year 2017 - 2018 [Member] | Short Tail [Member] | Catastrophe [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | (132)
North America Personal P&C Insurance [Member] | Accident Year 2017 to 2019 [Member] | Homeowners and Valuables [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 69 |  | 69 |
North America Personal P&C Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2018 [Member] | Homeowners and Valuables [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (36) |  | 82
Global Reinsurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (6) | (25) | (29) | (33)
Global Reinsurance [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (6) | (25) | (25) | (59)
Global Reinsurance [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | $ 0 | $ 0 | $ (4) | 26
Global Reinsurance [Member] | Accident year 2017 - 2018 [Member] | Short Tail [Member] | Catastrophe [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | $ 37

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Data Type: | na
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