Segments of Operations - Earnings before income taxes by segment and sub-segment (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	$ 258	$ 143
Realized gains (losses) on securities	77	(328)
Earnings (loss) from continuing operations before income taxes	335	(185)
Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	134	87
Investment and other income, net	154	84
Earnings before realized gains (losses) and income taxes	288	171
Other
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	(30)	(28)
Specialty Property and transportation \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	56	27
Specialty casualty \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	56	52
Specialty financial \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	25	17
Other specialty \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	(3)	(7)
Other lines \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	$ 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

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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.

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- Definition

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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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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