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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, 2023 | Sep. 30, 2022 | Sep. 30, 2023 | Sep. 30, 2022 | Jul. 01, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | $ (200) | $ (222) | $ (596) | $ (709) |  |  |
Unpaid losses and loss expenses | 79,705 | 75,336 | 79,705 | 75,336 |  | $ 75,747 | $ 72,330
Net loss and loss expenses paid, Prior Years |  |  | 10,158 | 9,217 |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease), Gross |  |  | 4,000 |  |  |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net | 61,897 | 58,023 | 61,897 | 58,023 |  | $ 58,661 | 56,198
Huatai Group |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Unpaid losses and loss expenses |  |  |  |  | $ 831 |  |
Liability for Unpaid Claims and Claims Adjustment Expense, Net |  |  |  |  | $ 405 |  | $ 0
Long Tail [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | 116 | 39 | 63 | (55) |  |  |
Short Tail [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | (316) | (261) | (659) | (654) |  |  |
North America Commercial P&C Insurance [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | (84) | (166) | (302) | (561) |  |  |
North America Commercial P&C Insurance [Member] | Long Tail [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | 107 | (29) | (23) | (315) |  |  |
North America Commercial P&C Insurance [Member] | Short Tail [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | (191) | (137) | (279) | (246) |  |  |
North America Commercial P&C Insurance [Member] | Commercial Excess and Umbrella [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development |  | 71 |  |  |  |  |
North America Commercial P&C Insurance [Member] | Workers' Compensation Insurance [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | 71 | (164) | 379 |  |  |  |
North America Commercial P&C Insurance [Member] | Property and Inland Marine |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development |  | (132) |  |  |  |  |
North America Commercial P&C Insurance [Member] | Auto Liability [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development |  | 58 |  |  |  |  |
North America Agricultural Insurance [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | (9) | 9 | (12) | (17) |  |  |
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 | (9) | 9 | (12) | (17) |  |  |
Corporate Segment [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development |  | 73 | 131 | 272 |  |  |
Corporate Segment [Member] | Long Tail [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | 61 | 73 | 131 | 272 |  |  |
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] | Long Tail [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development |  |  | 49 | 155 |  |  |
Overseas General Insurance [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | (49) | (5) | (253) | (238) |  |  |
Overseas General Insurance [Member] | Long Tail [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | (52) | (5) | (52) | (5) |  |  |
Overseas General Insurance [Member] | Short Tail [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | 3 | 0 | (201) | (233) |  |  |
Overseas General Insurance [Member] | Accident and Health Insurance Product Line [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development |  |  | 45 | (75) |  |  |
Overseas General Insurance [Member] | Property, Liability and Casualty Insurance Product Line |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development |  |  |  | (67) |  |  |
Overseas General Insurance [Member] | Property and Inland Marine |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development |  |  | 147 |  |  |  |
Overseas General Insurance [Member] | financial lines |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | 77 |  |  |  |  |  |
Overseas General Insurance [Member] | Political Risk |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | 51 |  |  |  |  |  |
North America Personal P&C Insurance [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | (119) | (133) | (135) | (187) |  |  |
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 | (119) | (133) | (135) | (187) |  |  |
Global Reinsurance [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | 0 | 0 | (25) | 22 |  |  |
Global Reinsurance [Member] | Long Tail [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | 0 | 0 | 7 | (7) |  |  |
Global Reinsurance [Member] | Short Tail [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | 0 | $ 0 | (32) | $ 29 |  |  |
North America Commercial P&C Insurance [Member] | Commercial Excess and Umbrella [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | 222 |  | 227 |  |  |  |
North America Commercial P&C Insurance [Member] | Property and Inland Marine |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | 188 |  | 113 |  |  |  |
North America Commercial P&C Insurance [Member] | Surety Product Line [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development |  |  | 101 |  |  |  |
North America Commercial P&C Insurance [Member] | Auto Liability [Member] |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development |  |  | 125 |  |  |  |
North American Personal P&C Insurance [Member] | Personal Excess Liability |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | 145 |  |  |  |  |  |
North American Personal P&C Insurance [Member] | homeowners and valuables lines |  |  |  |  |  |  |
Liability for Claims and Claims Adjustment Expense [Line Items] |  |  |  |  |  |  |
Net Prior Period Development | $ 263 |  | $ 244 |  |  |  |

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