Property and casualty insurance revenues derived from customers of foreign countries.

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Property and casualty insurance revenues derived from customers of foreign countries by subsidiary

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Net investment income plus other income less other expenses.

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Loss recognition charge from expected future losses on business

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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 related to the exit of certain lines of business within subsidiaries.

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Special charges to increase asbestos and environmental reserves

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Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

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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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Segments of Operations - Narrative (Details) $ in Millions	3 Months Ended		12 Months Ended
Segments of Operations - Narrative (Details) $ in Millions	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of segments \| segment			3
Percent of total revenue derived from sales of property and casualty insurance outside of the United States			5.00%	7.00%	7.00%
Net earned premiums			$ 5,099	$ 5,185	$ 4,865
Net investment income			2,132	2,303	2,094
Property and casualty insurance
Segment Reporting Information [Line Items]
Net earned premiums			5,099	5,185	4,865
Net investment income			399	472	438
Property and casualty insurance underwriting			224	212	302
Investment and other income, net			360	437	407
Property and casualty insurance \| Other lines
Segment Reporting Information [Line Items]
Net earned premiums			200	0	0
Property and casualty insurance underwriting			(202)	(113)	(20)
Special A&E charges	$ 47	$ 18	47	18	18
Other
Segment Reporting Information [Line Items]
Loss on the retirement of debt			5	5
Special charges to increase asbestos and environmental reserves			21	11	9
Run-off long-term care and life
Segment Reporting Information [Line Items]
Loss recognition charge			4
Special A&E charges
Segment Reporting Information [Line Items]
Special A&E charges			47	$ 18	18
Special A&E charges \| Property and casualty insurance \| Other lines
Segment Reporting Information [Line Items]
Special A&E charges			47		18
Neon Capital Limited
Segment Reporting Information [Line Items]
Net investment income			$ (5)
Neon Capital Limited \| Property and casualty insurance \| Other lines
Segment Reporting Information [Line Items]
Percent of foreign sales attributable to Neon			50.00%	66.67%
Net earned premiums				$ 384	306
Net investment income			$ (5)
Property and casualty insurance underwriting			(135)	(36)	$ (63)
Special charges related to the exit of certain lines of business within subsidiaries				$ 76
Investment and other income, net			$ (10)