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Unpaid losses and loss expenses Unpaid losses and loss expenses (narrative) (Detail) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | $ (167) | $ (243) | $ (559) | $ (643)
Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (252) | (246) | (514) | (319)
Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 85 | 3 | (45) | (324)
North America Commercial P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (109) | (216) | (425) | (472)
North America Commercial P&C Insurance [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (197) | (170) | (468) | (266)
North America Commercial P&C Insurance [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 88 | (46) | 43 | (206)
North America Commercial P&C Insurance [Member] | North America Workers' Compensation [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | (294) | (183)
North America Commercial P&C Insurance [Member] | Foreign Casualty Line [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | (39) | (28)
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 | (34) |  | (36) |
North America Commercial P&C Insurance [Member] | Auto Liability Excess Lines [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | 31 | 71
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 |  |  | (63) |
North America Commercial P&C Insurance [Member] | Other [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | (50)
North America Commercial P&C Insurance [Member] | Commercial Property and Marine [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (41) |  | (156)
North America Commercial P&C Insurance [Member] | Surety Product Line [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | (19)
North America Commercial P&C Insurance [Member] | Catastrophe [Member] | Property and Inland Marine [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (27) |  |  |
North America Commercial P&C Insurance [Member] | Non-catastrophe [Member] | Property and Inland Marine [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 116 |  |  |
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 2012 and prior [Member] | Commercial Excess and Umbrella [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (93) |  | (123)
North America Commercial P&C Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | North America Workers' Compensation [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | (56)
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] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Catastrophe [Member] | Other [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | (3)
North America Commercial P&C Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Catastrophe [Member] | Property and Inland Marine [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (42) |  | (157)
North America Commercial P&C Insurance [Member] | Accident years 2014 and prior [Member] | North America Workers' Compensation [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (45) |  | (127)
North America Commercial P&C Insurance [Member] | Accident years 2014 and prior [Member] | Foreign Casualty Line [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (28) |  |
North America Commercial P&C Insurance [Member] | Accident years 2017 - 2018 [Member] | Catastrophe [Member] | Property and Inland Marine [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] | Short-duration Insurance Contracts, Accident Year 2018 [Member] | North America Workers' Compensation [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 2017 and prior [Member] | Non-catastrophe [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 2015 and prior [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] | Accident year 2015 and prior [Member] | North America Workers' Compensation [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] | Foreign Casualty Line [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (39) |  |  |
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) |  |  |
North America Personal P&C Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (62) | 58 | (88) | 59
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 | (62) | 58 | (88) | 59
North America Personal P&C Insurance [Member] | Auto Liability and Marine [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | (16) |
North America Personal P&C Insurance [Member] | Non-catastrophe [Member] | Homeowners and Valuables [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 137 |  |
North America Personal P&C Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Homeowners and Valuables [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 80 |  |
North America Personal P&C Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Catastrophe [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | (68)
North America Personal P&C Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Catastrophe [Member] | Homeowners and Valuables [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (57) |  |
North America Personal P&C Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2015 [Member] | Personal lines [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (24) |  |
North America Personal P&C Insurance [Member] | Accident years 2017 - 2018 [Member] | Catastrophe [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | (132) |
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 |
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 Agricultural Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 18 | (1) | (43) | (77)
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 | (1) | (43) | (77)
North America Agricultural Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Catastrophe [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | (1)
Overseas General Insurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (25) | (72) | (49) | (166)
Overseas General Insurance [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (66) | (49) | (66) | (51)
Overseas General Insurance [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 41 | (23) | 17 | (115)
Overseas General Insurance [Member] | Political Risk [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (12) |  |
Overseas General Insurance [Member] | Aviation [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (10) |  |
Overseas General Insurance [Member] | Personal lines [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | (17)
Overseas General Insurance [Member] | Financial | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 50 | 38 |  |
Overseas General Insurance [Member] | Other [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (33) |  |
Overseas General Insurance [Member] | Other [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | (57)
Overseas General Insurance [Member] | Surety Product Line [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | (17)
Overseas General Insurance [Member] | Accident and Health Insurance Product Line [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | (16)
Overseas General Insurance [Member] | Energy Lines [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | (13)
Overseas General Insurance [Member] | Casualty Lines [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (101) | (54) |  |
Overseas General Insurance [Member] | Environmental Issue [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (10) |  |
Overseas General Insurance [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Catastrophe [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 4 |  | (8)
Overseas General Insurance [Member] | Accident years 2014 and prior [Member] | Financial | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (93) |  |
Overseas General Insurance [Member] | Accident years 2014 and prior [Member] | Casualty Lines [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (92) |  |
Overseas General Insurance [Member] | Accident years 2015 - 2017 [Member] | Financial | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 131 |  |
Overseas General Insurance [Member] | Accident years 2015 - 2017 [Member] | Casualty Lines [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 38 |  |
Overseas General Insurance [Member] | Accident years 2012 - 2015 [Member] | Marine [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (21) |  |
Overseas General Insurance [Member] | Accident years 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 years 2014 and 2016 [Member] | Property and Inland Marine [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  |  | (50)
Overseas General Insurance [Member] | Accident year 2015 and prior [Member] | Financial | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (75) |  |  |
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 years 2016 - 2018 [Member] | Financial | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 125 |  |  |
Overseas General Insurance [Member] | Accident years 2016 - 2018 [Member] | Casualty Lines [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 22 |  |  |
Global Reinsurance [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (25) | (24) | (33) | (54)
Global Reinsurance [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | (25) | (39) | (59) | (69)
Global Reinsurance [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 0 | 15 | 26 | 15
Global Reinsurance [Member] | Short-duration Insurance Contracts, Accident Year 2017 [Member] | Catastrophe [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 15 |  | 14
Global Reinsurance [Member] | Accident years 2017 - 2018 [Member] | Catastrophe [Member] | Short Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  |  | 37 |
Corporate Segment [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 36 | 12 | 79 | 67
Corporate Segment [Member] | Discontinued Operations [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 9 |  | 28 |
Corporate Segment [Member] | Long Tail [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | 36 | 12 | 79 | 67
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] | Environmental Issue [Member] |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development | $ 27 | $ 54 |  |

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