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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, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense | [1] | $ (1,153) | $ (986) | $ (414)
Prior Period Development, net Adjustments |  | 277 | 60 | 19
Net Prior Period Development |  | (876) | (926) | (395)
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 |  | 161 |  |
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 |  | 46 |  |
Colorado Wildfire |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 48 |  |
Long Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 58 | (44) | (313)
Short Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (934) | (882) | (82)
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 |  | (1,285) |  |
Other PPD adjustments | [2] | (440) |  |
Prior Period Development, net Adjustments |  | 111 |  |
Net Prior Period Development |  | (1,174) |  |
Segments included in loss triangles [Domain] | Accident years prior to 2013 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (7) |  |
Segments included in loss triangles [Domain] | 2013 - 2021 accident years (implied PPD per loss triangles) |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (838) |  |
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 |  | (674) |  |
Other PPD adjustments | [2],[3] | (283) |  |
Prior Period Development, net Adjustments | [4] | 112 |  |
Net Prior Period Development |  | (562) | (762) | (702)
North America Commercial P&C Insurance [Member] | Accident years prior to 2013 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 11 |  |
North America Commercial P&C Insurance [Member] | 2013 - 2021 accident years (implied PPD per loss triangles) |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (402) |  |
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 |  | (314) |  |
Other PPD adjustments | [2] | (253) |  |
Prior Period Development, net Adjustments |  | 85 |  |
Net Prior Period Development |  | (229) | (482) | (672)
North America Commercial P&C Insurance [Member] | Long Tail [Member] | Accident years prior to 2013 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 22 |  |
North America Commercial P&C Insurance [Member] | Long Tail [Member] | 2013 - 2021 accident years (implied PPD per loss triangles) |  |  |  |
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] | 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 |  | (360) |  |
Other PPD adjustments | [2] | (30) |  |
Prior Period Development, net Adjustments |  | 27 |  |
Net Prior Period Development |  | (333) | (280) | (30)
North America Commercial P&C Insurance [Member] | Short Tail [Member] | Accident years prior to 2013 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (11) |  |
North America Commercial P&C Insurance [Member] | Short Tail [Member] | 2013 - 2021 accident years (implied PPD per loss triangles) |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (319) |  |
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 |  | (186) | (305) | 63
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 |  | (186) |  |
Other PPD adjustments | [2],[5] | (58) |  |
Prior Period Development, net Adjustments |  | 0 |  |
Net Prior Period Development |  | (186) | (305) | 63
North America Personal P&C Insurance [Member] | Short Tail [Member] | Accident years prior to 2013 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (5) |  |
North America Personal P&C Insurance [Member] | Short Tail [Member] | 2013 - 2021 accident years (implied PPD per loss triangles) |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (123) |  |
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 |  | (448) |  |
Other PPD adjustments | [2],[6] | (100) |  |
Prior Period Development, net Adjustments |  | 0 |  |
Net Prior Period Development |  | (448) | (441) | (150)
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 |  | 105 |  |
Overseas General Insurance [Member] | Accident years prior to 2013 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (2) |  |
Overseas General Insurance [Member] | 2013 - 2021 accident years (implied PPD per loss triangles) |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (346) |  |
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 |  | (65) |  |
Other PPD adjustments | [2] | 3 |  |
Prior Period Development, net Adjustments |  | 0 |  |
Net Prior Period Development |  | (65) | (106) | (49)
Overseas General Insurance [Member] | Long Tail [Member] | Accident years prior to 2013 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 8 |  |
Overseas General Insurance [Member] | Long Tail [Member] | 2013 - 2021 accident years (implied PPD per loss triangles) |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (76) |  |
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 |  | (383) |  |
Other PPD adjustments | [2] | (103) |  |
Prior Period Development, net Adjustments |  | 0 |  |
Net Prior Period Development |  | (383) | (335) | (101)
Overseas General Insurance [Member] | Short Tail [Member] | Accident years prior to 2013 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (10) |  |
Overseas General Insurance [Member] | Short Tail [Member] | 2013 - 2021 accident years (implied PPD per loss triangles) |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (270) |  |
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 |  | 23 |  |
Other PPD adjustments | [2] | 1 |  |
Prior Period Development, net Adjustments |  | (1) |  |
Net Prior Period Development |  | 22 | 3 | (29)
Global Reinsurance [Member] | Accident years prior to 2013 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (11) |  |
Global Reinsurance [Member] | 2013 - 2021 accident years (implied PPD per loss triangles) |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 33 |  |
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 | [2] | 1 |  |
Prior Period Development, net Adjustments |  | 0 |  |
Net Prior Period Development |  | (7) | (25) | (25)
Global Reinsurance [Member] | Long Tail [Member] | Accident years prior to 2013 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (7) |  |
Global Reinsurance [Member] | Long Tail [Member] | 2013 - 2021 accident years (implied PPD per loss triangles) |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (1) |  |
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 |  | 30 |  |
Other PPD adjustments | [2] | 0 |  |
Prior Period Development, net Adjustments |  | (1) |  |
Net Prior Period Development |  | 29 | 28 | (4)
Global Reinsurance [Member] | Short Tail [Member] | Accident years prior to 2013 |  |  |  |
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] | Short Tail [Member] | 2013 - 2021 accident years (implied PPD per loss triangles) |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 34 |  |
North America Agricultural Insurance [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (61) | 10 | (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 |  | (227) |  |
Prior Period Development, net Adjustments |  | 166 |  |
Net Prior Period Development |  | (61) | 10 | (10)
Corporate Segment [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 359 | 569 | 433
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 |  | 359 |  |
Prior Period Development, net Adjustments |  | 0 |  |
Net Prior Period Development |  | 359 | 569 | 433
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] | Relates to prior period loss reserve development only and excludes prior period development related to reinstatement premiums, expense adjustments, and earned premiums totaling $277 million, $60 million, and $19 million for 2022, 2021, and 2020, respectively.
[2] | Other includes the impact of foreign exchange.
[3] | Includes favorable development of $161 million related to our Alternative Risk Solutions business (U.S. and Bermuda) and an adjustment to exclude $46 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.
[4] | Includes premium returns associated with our Alternative Risk Solutions business, which is excluded from the triangles.
[5] | Includes $48 million relating to the Colorado Wildfire CAT event that began December 30, 2021.
[6] | Includes favorable development of $105 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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