Segments of Operations - Earnings before income taxes by segment and sub-segment (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	$ 290	$ 310
Realized gains (losses) on securities	14	(46)
Earnings before income taxes	304	264
Operating Segments \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	153	154
Investment and other income, net	187	196
Earnings before realized gains (losses) and income taxes	340	350
Operating Segments \| Property and Casualty Insurance \| Property and transportation
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	56	43
Operating Segments \| Property and Casualty Insurance \| Specialty casualty
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	74	88
Operating Segments \| Property and Casualty Insurance \| Specialty financial
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	33	26
Operating Segments \| Property and Casualty Insurance \| Other specialty
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	(9)	(2)
Operating Segments \| Property and Casualty Insurance \| Other lines
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	(1)	(1)
Operating Segments \| Other
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	$ (50)	$ (40)

Net investment income plus other income less other expenses.

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- Definition

The net result for the period of deducting operating expenses from operating revenues (excluding realized gains (losses) on securities and subsidiaries) before income taxes.

+ References

No definition available.

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- Definition

Underwriting income (loss) for the property and casualty insurance segment, which is calculated as premiums earned less losses and loss adjustment expenses less commissions and other underwriting expenses.

+ References

No definition available.

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- Definition

Amount of realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

+ References

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- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-22

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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-Name Accounting Standards Codification
-Section 50
-Paragraph 30
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-30

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 32
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 31
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-31

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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-Name Accounting Standards Codification
-Section 50
-Paragraph 32
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482810/280-10-50-32

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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