Segments of Operations - Earnings before income taxes by segment and sub-segment (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	$ 242	$ 245	$ 809	$ 920
Realized gains (losses) on securities	(19)	(35)	(67)	(143)
Realized loss on subsidiary	(4)	0	(4)	0
Earnings before income taxes	219	210	738	777
Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	142	155	420	558
Investment and other income, net	156	134	527	498
Earnings before realized gains (losses) and income taxes	298	289	947	1,056
Other
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	(56)	(44)	(138)	(136)
Property and transportation \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	42	39	117	140
Specialty casualty \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	78	118	261	372
Specialty financial \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	29	15	65	81
Other specialty \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	(6)	(14)	(22)	(30)
Other lines \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	$ (1)	$ (3)	$ (1)	$ (5)

Net investment income plus other income less other expenses.

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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.

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

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