Segments of Operations - Earnings before income taxes by segment and sub-segment (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	$ 536	$ 821	$ 905
Realized gains (losses) on securities	289	287	(266)
Subsidiaries	23	0	0
Earnings before income taxes	848	1,108	639
Property and casualty insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	224	212	302
Investment and other income, net	360	437	407
Earnings before realized gains (losses) and income taxes	584	649	709
Annuity
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	171	362	361
Other
Segment Reporting Information [Line Items]
Earnings before realized gains (losses) and income taxes	(219)	(190)	(165)
Property and transportation \| Property and casualty insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	181	79	120
Specialty casualty \| Property and casualty insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	223	175	141
Specialty financial \| Property and casualty insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	50	92	66
Other specialty \| Property and casualty insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	(28)	(21)	(5)
Other lines \| Property and casualty insurance
Segment Reporting Information [Line Items]
Property and casualty insurance underwriting	$ (202)	$ (113)	$ (20)

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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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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