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Unpaid losses and loss expenses (A&E Loss Roll-forward) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2023 | Dec. 31, 2022 | Dec. 31, 2021
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (gross) at beginning of year |  | $ 1,510 | $ 1,628 | $ 1,868
Balance (net) at beginning of year |  | 1,013 | 1,102 | 1,252
Incurred activity, gross |  | 268 | 212 | 148
Incurred activity, net | [1] | 183 | 132 | 104
Paid activity, gross |  | (363) | (330) | (388)
Paid activity, net |  | (251) | (221) | (254)
Balance (gross) at end of year |  | 1,415 | 1,510 | 1,628
Balance (net) at end of year |  | 945 | 1,013 | 1,102
Brandywine Run-off [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Contributions to the dividend retention fund |  | 75 | 75 |
Asbestos Issue [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (gross) at beginning of year |  | 1,098 | 1,226 | 1,351
Balance (net) at beginning of year |  | 703 | 800 | 873
Incurred activity, gross |  | 180 | 87 | 96
Incurred activity, net |  | 120 | 55 | 64
Paid activity, gross |  | (258) | (215) | (221)
Paid activity, net |  | (169) | (152) | (137)
Balance (gross) at end of year |  | 1,020 | 1,098 | 1,226
Balance (net) at end of year |  | 654 | 703 | 800
Environmental Issue [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (gross) at beginning of year |  | 412 | 402 | 517
Balance (net) at beginning of year |  | 310 | 302 | 379
Incurred activity, gross |  | 88 | 125 | 52
Incurred activity, net |  | 63 | 77 | 40
Paid activity, gross |  | (105) | (115) | (167)
Paid activity, net |  | (82) | (69) | (117)
Balance (gross) at end of year |  | 395 | 412 | 402
Balance (net) at end of year |  | 291 | 310 | $ 302
Brandywine [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (net) at beginning of year |  | 602 |  |
Balance (net) at end of year |  | 570 | 602 |
Westchester Specialty [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (net) at beginning of year |  | 98 |  |
Balance (net) at end of year |  | 89 | 98 |
Other Segments [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (net) at beginning of year |  | 47 |  |
Balance (net) at end of year |  | 45 | 47 |
The Chubb Corporation [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (net) at beginning of year |  | 266 |  |
Balance (net) at end of year |  | $ 241 | $ 266 |
[1] | Excludes unallocated loss expenses and the net activity reflects third-party reinsurance other than the aggregate excess of loss reinsurance provided by National Indemnity Company (NICO) to Westchester Specialty (see Westchester Specialty section below)

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