Segments of Operations - Narrative (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) segment	Sep. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of segments \| segment			3
Net earned premiums	$ 1,381	$ 1,442	$ 3,774	$ 3,815
Net investment income	572	588	1,584	1,710
Property and Casualty Insurance
Segment Reporting Information [Line Items]
Net earned premiums	1,381	1,442	3,774	3,815
Net investment income	112	124	277	352
Property and casualty insurance underwriting	18	54	114	200
Investment and other income, net	100	118	249	328
Other
Segment Reporting Information [Line Items]
Special charges to increase asbestos and environmental reserves	21	11
Run-off Long-term Care and Life
Segment Reporting Information [Line Items]
Loss recognition charge	4
Other lines \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Net earned premiums	42	0	174	0
Property and casualty insurance underwriting	(86)	(34)	(133)	(36)
Special A&E charges	47	18	47	18
Neon Capital Limited
Segment Reporting Information [Line Items]
Net investment income	1		(5)
Neon Capital Limited \| Other lines \| Property and Casualty Insurance
Segment Reporting Information [Line Items]
Net earned premiums		97		274
Net investment income	1		(5)
Property and casualty insurance underwriting	(38)	$ (19)	(82)	$ (33)
Investment and other income, net	$ (2)		$ (10)

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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Special charges to increase asbestos and environmental reserves

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Amount, after effects of reinsurance, of expense for claims incurred and costs incurred in the claim settlement process attributable to asbestos and environmental claims.

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Amount, after investment expense, of income earned from investments in securities and real estate. Includes, but is not limited to, real estate investment, policy loans, dividends, and interest. Excludes realized gain (loss) on investments.

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Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

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Amount, after premiums ceded to other entities and premiums assumed by the entity, of property and casualty premiums earned.

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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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