Investments (Net investment income) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Net Investment Income [Line Items]
Gross investment income	$ 346	$ 587
Investment expense	(17)	(16)
Net investment income	329	571
Fixed maturity securities
Net Investment Income [Line Items]
Gross investment income	438	455
Equity securities
Net Investment Income [Line Items]
Gross investment income	(44)	30
Limited partnership investments
Net Investment Income [Line Items]
Gross investment income	(70)	76
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	14	12
Short term investments
Net Investment Income [Line Items]
Gross investment income	7	10
Trading portfolio
Net Investment Income [Line Items]
Gross investment income	1	2
Other
Net Investment Income [Line Items]
Gross investment income	$ 0	$ 2

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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-SubTopic 220
-Section S99
-Paragraph 1
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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
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-Paragraph 2
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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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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