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Unpaid losses and loss expenses (A&E Loss Roll-forward) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021 | Dec. 31, 2020
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (gross) at beginning of year |  | $ 1,628 | $ 1,868 | $ 1,988
Balance (net) at beginning of year |  | 1,102 | 1,252 | 1,326
Incurred activity, gross |  | 212 | 148 | 229
Incurred activity, net | [1] | 132 | 104 | 131
Paid activity, gross |  | (330) | (388) | (349)
Paid activity, net |  | (221) | (254) | (205)
Balance (gross) at end of year |  | 1,510 | 1,628 | 1,868
Balance (net) at end of year |  | 1,013 | 1,102 | 1,252
Asbestos Issue [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (gross) at beginning of year |  | 1,226 | 1,351 | 1,459
Balance (net) at beginning of year |  | 800 | 873 | 916
Incurred activity, gross |  | 87 | 96 | 150
Incurred activity, net |  | 55 | 64 | 90
Paid activity, gross |  | (215) | (221) | (258)
Paid activity, net |  | (152) | (137) | (133)
Balance (gross) at end of year |  | 1,098 | 1,226 | 1,351
Balance (net) at end of year |  | 703 | 800 | 873
Environmental Issue [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (gross) at beginning of year |  | 402 | 517 | 529
Balance (net) at beginning of year |  | 302 | 379 | 410
Incurred activity, gross |  | 125 | 52 | 79
Incurred activity, net |  | 77 | 40 | 41
Paid activity, gross |  | (115) | (167) | (91)
Paid activity, net |  | (69) | (117) | (72)
Balance (gross) at end of year |  | 412 | 402 | 517
Balance (net) at end of year |  | 310 | 302 | $ 379
Brandywine [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (net) at beginning of year |  | 646 |  |
Balance (net) at end of year |  | 602 | 646 |
Westchester Specialty [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (net) at beginning of year |  | 100 |  |
Balance (net) at end of year |  | 98 | 100 |
Other Segments [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (net) at beginning of year |  | 70 |  |
Balance (net) at end of year |  | 47 | 70 |
The Chubb Corporation [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (net) at beginning of year |  | 286 |  |
Balance (net) at end of year |  | $ 266 | $ 286 |
[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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- Definition Carrying amount as of the balance sheet date of reserves for the costs of settling insured claims and costs incurred in the claims settlement process attributable to asbestos and environmental claims, before estimated recoveries from reinsurers. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (cc) -URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 50 -Paragraph 3 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
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