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Unpaid losses and loss expenses (A&E Loss Roll-forward) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (gross) at beginning of year |  | $ 2,117 | $ 2,228 | $ 2,303
Balance (net) at beginning of year |  | 1,447 | 1,527 | 1,609
Incurred activity, gross |  | 175 | 237 | 427
Incurred activity, net | [1] | 98 | (22) | 217
Paid activity, gross |  | (304) | (348) | (502)
Paid activity, net |  | (219) | (58) | (299)
Balance (gross) at end of year |  | 1,988 | 2,117 | 2,228
Balance (net) at end of year |  | 1,326 | 1,447 | 1,527
Asbestos Issue [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (gross) at beginning of year |  | 1,492 | 1,621 | 1,726
Balance (net) at beginning of year |  | 964 | 1,051 | 1,119
Incurred activity, gross |  | 129 | 136 | 228
Incurred activity, net |  | 70 | 75 | 104
Paid activity, gross |  | (162) | (265) | (333)
Paid activity, net |  | (118) | (162) | (172)
Balance (gross) at end of year |  | 1,459 | 1,492 | 1,621
Balance (net) at end of year |  | 916 | 964 | 1,051
Environmental Issue [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (gross) at beginning of year |  | 625 | 607 | 577
Balance (net) at beginning of year |  | 483 | 476 | 490
Incurred activity, gross |  | 46 | 101 | 199
Incurred activity, net |  | 28 | (97) | 113
Paid activity, gross |  | (142) | (83) | (169)
Liability for Unpaid Claims and Claims Adjustment Expense, Period Increase (Decrease) |  | (101) | 104 | (127)
Balance (gross) at end of year |  | 529 | 625 | 607
Balance (net) at end of year |  | 410 | 483 | $ 476
Brandywine [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (net) at beginning of year |  | 807 |  |
Balance (net) at end of year |  | 754 | 807 |
Westchester Specialty [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (net) at beginning of year |  | 120 |  |
Balance (net) at end of year |  | 117 | 120 |
Other Segments [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (net) at beginning of year |  | 78 |  |
Balance (net) at end of year |  | 74 | 78 |
The Chubb Corporation [Member] |  |  |  |
Liability For Asbestos And Environmental Claims Net Roll Forward |  |  |  |
Balance (net) at beginning of year |  | 442 |  |
Balance (net) at end of year |  | $ 381 | $ 442 |
[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 http://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 http://asc.fasb.org/extlink&oid=116884095&loc=d3e14764-158437 + Details
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