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Business segment data - Insurance premiums by type (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Property/Casualty [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Premiums written - Direct | $ 65,495 | $ 61,990 | $ 56,700
Premiums written - Assumed | 20,422 | 20,751 | 15,143
Premiums written - Ceded | (2,231) | (2,402) | (1,155)
Premiums written | 83,686 | 80,339 | 70,688
Premiums earned - Direct | 64,880 | 60,437 | 55,879
Premiums earned - Assumed | 20,738 | 20,442 | 14,184
Premiums earned - Ceded | (2,359) | (2,548) | (1,293)
Premiums earned | 83,259 | 78,331 | 68,770
Life/Health [Member] |  |  |
Segment Reporting Information [Line Items] |  |  |
Premiums written - Direct | 19 |  | 582
Premiums written - Assumed | 5,016 | 5,126 | 5,222
Premiums written - Ceded | (28) | (33) | (37)
Premiums written | 5,007 | 5,093 | 5,767
Premiums earned - Direct | 18 |  | 582
Premiums earned - Assumed | 5,008 | 5,105 | 5,263
Premiums earned - Ceded | (28) | (33) | (39)
Premiums earned | $ 4,998 | $ 5,072 | $ 5,806

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- Definition Amount of earned premiums assumed from other entities. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 235 -Name Accounting Standards Codification -Section S99 -Paragraph 2 -Subparagraph (SX 210.12-17(Column D)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477965/944-235-S99-2 Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(1)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147477250/944-220-S99-1 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479032/944-605-50-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479032/944-605-50-1 + Details
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- Definition Amount of written premiums assumed from other entities. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 605 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (b)(2) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479032/944-605-50-1 + Details
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