Segments of Operations - Earnings before income taxes by segment and sub-segment (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	$ 257	$ 299	$ 567	$ 675
Realized gains (losses) on securities	(2)	(93)	(48)	(108)
Earnings before income taxes	255	206	519	567
Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	124	196	278	403
Investment and other income, net	175	149	371	364
Earnings before realized gains (losses) and income taxes	299	345	649	767
Other
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	(42)	(46)	(82)	(92)
Property and transportation \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	32	39	75	101
Specialty casualty \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	95	130	183	254
Specialty financial \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	10	37	36	66
Other specialty \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	(14)	(9)	(16)	(16)
Other lines \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	$ 1	$ (1)	$ 0	$ (2)

Net investment income plus other income less other expenses.

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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

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

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

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
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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.

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