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Unpaid losses and loss expenses Unpaid losses and loss expenses (Supplementary PPD Reconciliation) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | $ (882) |  |
Prior Period Development, net Adjustments |  | 83 | $ 232 | $ 30
Net Prior Period Development |  | (773) | (876) | (926)
Prior Period Development, net adjustments except related to A&H |  | 109 |  |
Alternative Risk Solutions [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 88 |  |
North America Workers' Compensation [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 92 |  |
Long Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 148 | 58 | (44)
Short Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (921) | (934) | (882)
Segments included in loss triangles [Domain] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (1,135) |  |
Other PPD adjustments | [1] | (285) |  |
Prior Period Development, net Adjustments |  | 103 |  |
Net Prior Period Development |  | (1,032) |  |
Segments included in loss triangles [Domain] | 2014 - 2022 accident years |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (735) |  |
Segments included in loss triangles [Domain] | Accident years prior to 2014 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (115) |  |
North America Commercial P&C Insurance [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (592) |  |
Other PPD adjustments | [1],[2] | (222) |  |
Prior Period Development, net Adjustments | [3] | 98 |  |
Net Prior Period Development |  | (494) | (562) | (762)
North America Commercial P&C Insurance [Member] | 2014 - 2022 accident years |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (294) |  |
North America Commercial P&C Insurance [Member] | Accident years prior to 2014 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (76) |  |
North America Commercial P&C Insurance [Member] | Long Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (176) |  |
Other PPD adjustments | [1] | (187) |  |
Prior Period Development, net Adjustments |  | 90 |  |
Net Prior Period Development |  | (86) | (229) | (482)
North America Commercial P&C Insurance [Member] | Long Tail [Member] | 2014 - 2022 accident years |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 83 |  |
North America Commercial P&C Insurance [Member] | Long Tail [Member] | Accident years prior to 2014 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (72) |  |
North America Commercial P&C Insurance [Member] | Short Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (416) |  |
Other PPD adjustments | [1] | (35) |  |
Prior Period Development, net Adjustments |  | 8 |  |
Net Prior Period Development |  | (408) | (333) | (280)
North America Commercial P&C Insurance [Member] | Short Tail [Member] | 2014 - 2022 accident years |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (377) |  |
North America Commercial P&C Insurance [Member] | Short Tail [Member] | Accident years prior to 2014 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (4) |  |
North America Personal P&C Insurance [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (134) | (186) | (305)
North America Personal P&C Insurance [Member] | Long Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 0 | 0 | 0
North America Personal P&C Insurance [Member] | Short Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (132) |  |
Other PPD adjustments | [1] | (4) |  |
Prior Period Development, net Adjustments |  | (2) |  |
Net Prior Period Development |  | (134) | (186) | (305)
North America Personal P&C Insurance [Member] | Short Tail [Member] | 2014 - 2022 accident years |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (131) |  |
North America Personal P&C Insurance [Member] | Short Tail [Member] | Accident years prior to 2014 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 3 |  |
Overseas General Insurance [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (376) |  |
Other PPD adjustments | [1],[4] | (60) |  |
Prior Period Development, net Adjustments |  | 0 |  |
Net Prior Period Development |  | (376) | (448) | (441)
Overseas General Insurance [Member] | International A&H [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 56 |  |
Overseas General Insurance [Member] | 2014 - 2022 accident years |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (290) |  |
Overseas General Insurance [Member] | Accident years prior to 2014 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (26) |  |
Overseas General Insurance [Member] | Long Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (50) |  |
Other PPD adjustments | [1] | (2) |  |
Prior Period Development, net Adjustments |  | 0 |  |
Net Prior Period Development |  | (50) | (65) | (106)
Overseas General Insurance [Member] | Long Tail [Member] | 2014 - 2022 accident years |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (26) |  |
Overseas General Insurance [Member] | Long Tail [Member] | Accident years prior to 2014 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (22) |  |
Overseas General Insurance [Member] | Short Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (326) |  |
Other PPD adjustments | [1] | (58) |  |
Prior Period Development, net Adjustments |  | 0 |  |
Net Prior Period Development |  | (326) | (383) | (335)
Overseas General Insurance [Member] | Short Tail [Member] | 2014 - 2022 accident years |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (264) |  |
Overseas General Insurance [Member] | Short Tail [Member] | Accident years prior to 2014 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (4) |  |
Global Reinsurance [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (35) |  |
Other PPD adjustments | [1] | 1 |  |
Prior Period Development, net Adjustments |  | 7 |  |
Net Prior Period Development |  | (28) | 22 | 3
Global Reinsurance [Member] | 2014 - 2022 accident years |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (20) |  |
Global Reinsurance [Member] | Accident years prior to 2014 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (16) |  |
Global Reinsurance [Member] | Long Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 7 |  |
Other PPD adjustments | [1] | 1 |  |
Prior Period Development, net Adjustments |  | 0 |  |
Net Prior Period Development |  | 7 | (7) | (25)
Global Reinsurance [Member] | Long Tail [Member] | 2014 - 2022 accident years |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 22 |  |
Global Reinsurance [Member] | Long Tail [Member] | Accident years prior to 2014 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (16) |  |
Global Reinsurance [Member] | Short Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (42) |  |
Other PPD adjustments | [1] | 0 |  |
Prior Period Development, net Adjustments |  | 7 |  |
Net Prior Period Development |  | (35) | 29 | 28
Global Reinsurance [Member] | Short Tail [Member] | 2014 - 2022 accident years |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (42) |  |
Global Reinsurance [Member] | Short Tail [Member] | Accident years prior to 2014 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 0 |  |
North America Agricultural Insurance [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (18) | (61) | 10
North America Agricultural Insurance [Member] | Long Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 0 | 0 | 0
North America Agricultural Insurance [Member] | Short Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (24) |  |
Prior Period Development, net Adjustments |  | 6 |  |
Net Prior Period Development |  | (18) | (61) | 10
Corporate Segment [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 277 | 359 | 569
Corporate Segment [Member] | Long Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 277 |  |
Prior Period Development, net Adjustments |  | 0 |  |
Net Prior Period Development |  | 277 | 359 | 569
Corporate Segment [Member] | Short Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | $ 0 | $ 0 | $ 0
[1] | Other includes the impact of foreign exchange.
[2] | Includes favorable development of $88 million related to our Alternative Risk Solutions business (U.S. and Bermuda) and an adjustment to exclude $92 million in unfavorable development in the workers' compensation line, associated with an increase in exposure for which additional premiums were collected; the remaining difference relates to a number of other items, none of which are individually material.
[3] | Includes premium returns associated with our Alternative Risk Solutions business, which is excluded from the triangles.
[4] | Includes favorable development of $56 million related to International A&H business; the remaining difference relates to a number of other items, none of which are individually material.

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