Investments (Net investment income) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Investment Income [Line Items]
Gross investment income	$ 1,878	$ 2,093	$ 2,047
Investment expense	(61)	(59)	(59)
Net investment income	1,817	2,034	1,988
Fixed maturity securities
Net Investment Income [Line Items]
Gross investment income	1,795	1,812	1,819
Equity securities
Net Investment Income [Line Items]
Gross investment income	18	12	10
Limited partnership investments
Net Investment Income [Line Items]
Gross investment income	(22)	207	155
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	50	34	41
Short term investments
Net Investment Income [Line Items]
Gross investment income	26	15	8
Trading portfolio
Net Investment Income [Line Items]
Gross investment income	7	12	10
Other
Net Investment Income [Line Items]
Gross investment income	$ 4	$ 1	$ 4

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
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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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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