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Unpaid losses and loss expenses Unpaid losses and loss expenses (Details) (Supplementary PPD Reconciliation) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense | [1] | $ (986) | $ (414) | $ (845)
Prior Period Development, net Adjustments |  | 60 | 19 | 53
Net Prior Period Development |  | (926) | (395) | (792)
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 |  | (96) |  |
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 |  | (48) |  |
Long Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (44) | (313) | (642)
Short Tail [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | (882) | (82) | (150)
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 |  | (1,593) |  |
Other PPD adjustments | [2] | (296) |  |
Prior Period Development, net Adjustments |  | 88 |  |
Net Prior Period Development |  | (1,505) |  |
Segments included in loss triangles [Domain] | prior to 2012 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (309) |  |
Segments included in loss triangles [Domain] | 2012 - 2020 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (988) |  |
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 |  | (841) |  |
Other PPD adjustments | [2],[3] | (152) |  |
Prior Period Development, net Adjustments | [4] | 79 |  |
Net Prior Period Development |  | (762) | (702) | (649)
North America Commercial P&C Insurance [Member] | prior to 2012 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (194) |  |
North America Commercial P&C Insurance [Member] | 2012 - 2020 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (495) |  |
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 |  | (551) |  |
Other PPD adjustments | [2] | (142) |  |
Prior Period Development, net Adjustments |  | 69 |  |
Net Prior Period Development |  | (482) | (672) | (668)
North America Commercial P&C Insurance [Member] | Long Tail [Member] | prior to 2012 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (191) |  |
North America Commercial P&C Insurance [Member] | Long Tail [Member] | 2012 - 2020 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (218) |  |
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 |  | (290) |  |
Other PPD adjustments | [2] | (10) |  |
Prior Period Development, net Adjustments |  | 10 |  |
Net Prior Period Development |  | (280) | (30) | 19
North America Commercial P&C Insurance [Member] | Short Tail [Member] | prior to 2012 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (3) |  |
North America Commercial P&C Insurance [Member] | Short Tail [Member] | 2012 - 2020 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (277) |  |
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 |  | (305) | 63 | (95)
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 |  | (304) |  |
Other PPD adjustments | [2] | (9) |  |
Prior Period Development, net Adjustments |  | (1) |  |
Net Prior Period Development |  | (305) | 63 | (95)
North America Personal P&C Insurance [Member] | Short Tail [Member] | prior to 2012 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (2) |  |
North America Personal P&C Insurance [Member] | Short Tail [Member] | 2012 - 2020 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (293) |  |
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],[5] | (134) |  |
Prior Period Development, net Adjustments |  | 7 |  |
Net Prior Period Development |  | (441) | (150) | (92)
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 |  | (118) |  |
Overseas General Insurance [Member] | prior to 2012 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (82) |  |
Overseas General Insurance [Member] | 2012 - 2020 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (232) |  |
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 |  | (106) |  |
Other PPD adjustments | [2] | (8) |  |
Prior Period Development, net Adjustments |  | 0 |  |
Net Prior Period Development |  | (106) | (49) | (68)
Overseas General Insurance [Member] | Long Tail [Member] | prior to 2012 |  |  |  |
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] | Long Tail [Member] | 2012 - 2020 |  |  |  |
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 |  | (342) |  |
Other PPD adjustments | [2] | (126) |  |
Prior Period Development, net Adjustments |  | 7 |  |
Net Prior Period Development |  | (335) | (101) | (24)
Overseas General Insurance [Member] | Short Tail [Member] | prior to 2012 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (6) |  |
Overseas General Insurance [Member] | Short Tail [Member] | 2012 - 2020 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (210) |  |
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 |  | 0 |  |
Other PPD adjustments | [2] | (1) |  |
Prior Period Development, net Adjustments |  | 3 |  |
Net Prior Period Development |  | 3 | (29) | (29)
Global Reinsurance [Member] | prior to 2012 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (31) |  |
Global Reinsurance [Member] | 2012 - 2020 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | 32 |  |
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 |  | (28) |  |
Other PPD adjustments | [2] | 1 |  |
Prior Period Development, net Adjustments |  | 3 |  |
Net Prior Period Development |  | (25) | (25) | (59)
Global Reinsurance [Member] | Long Tail [Member] | prior to 2012 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (27) |  |
Global Reinsurance [Member] | Long Tail [Member] | 2012 - 2020 |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Prior Year Claims and Claims Adjustment Expense |  | (2) |  |
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 |  | 28 |  |
Other PPD adjustments | [2] | (2) |  |
Prior Period Development, net Adjustments |  | 0 |  |
Net Prior Period Development |  | 28 | (4) | 30
Global Reinsurance [Member] | Short Tail [Member] | prior to 2012 |  |  |  |
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] | 2012 - 2020 |  |  |  |
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 |  | 10 | (10) | (80)
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 |  | 38 |  |
Prior Period Development, net Adjustments |  | (28) |  |
Net Prior Period Development |  | 10 | (10) | (80)
Corporate Segment [Member] |  |  |  |
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items] |  |  |  |
Net Prior Period Development |  | 569 | 433 | 153
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 |  | 569 |  |
Prior Period Development, net Adjustments |  | 0 |  |
Net Prior Period Development |  | 569 | 433 | 153
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 $60 million, $19 million, and $53 million for 2021, 2020, and 2019, respectively.
[2] | Other includes the impact of foreign exchange.
[3] | Includes favorable development of $96 million related to our Alternative Risk Solutions business (U.S. and Bermuda) and an adjustment to exclude $48 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 favorable development of $118 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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