Investments (Net investment income) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Net Investment Income [Line Items]
Gross investment income	$ 521	$ 346
Investment expense	(17)	(17)
Net investment income	504	329
Fixed maturity securities
Net Investment Income [Line Items]
Gross investment income	428	438
Equity securities
Net Investment Income [Line Items]
Gross investment income	29	(44)
Limited partnership investments
Net Investment Income [Line Items]
Gross investment income	43	(70)
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	14	14
Short term investments
Net Investment Income [Line Items]
Gross investment income	0	7
Trading portfolio
Net Investment Income [Line Items]
Gross investment income	5	1
Other
Net Investment Income [Line Items]
Gross investment income	$ 2	$ 0

Amount, before 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.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.2)
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Amount of expenses related to the generation of investment income.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 944
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-Section S99
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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-Paragraph 1
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