Investments (Net investment income) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net Investment Income [Line Items]
Gross investment income	$ 2,181	$ 1,878	$ 2,093
Investment expense	(63)	(61)	(59)
Net investment income	2,118	1,817	2,034
Fixed maturity securities
Net Investment Income [Line Items]
Gross investment income	1,817	1,795	1,812
Equity securities
Net Investment Income [Line Items]
Gross investment income	85	18	12
Limited partnership investments
Net Investment Income [Line Items]
Gross investment income	180	(22)	207
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	51	50	34
Short term investments
Net Investment Income [Line Items]
Gross investment income	34	26	15
Trading portfolio
Net Investment Income [Line Items]
Gross investment income	9	7	12
Other
Net Investment Income [Line Items]
Gross investment income	$ 5	$ 4	$ 1

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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Reference 1: 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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