Investments (Net investment income) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Net Investment Income [Line Items]
Gross investment income	$ 503	$ 501	$ 1,621	$ 1,528
Investment expense	(16)	(14)	(48)	(45)
Net investment income	487	487	1,573	1,483
Fixed maturity securities
Net Investment Income [Line Items]
Gross investment income	452	449	1,362	1,339
Equity securities
Net Investment Income [Line Items]
Gross investment income	16	10	62	32
Limited partnership investments
Net Investment Income [Line Items]
Gross investment income	12	23	125	93
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	13	11	37	36
Short term investments
Net Investment Income [Line Items]
Gross investment income	8	6	27	18
Trading portfolio
Net Investment Income [Line Items]
Gross investment income	2	1	6	6
Other
Net Investment Income [Line Items]
Gross investment income	$ 0	$ 1	$ 2	$ 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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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
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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

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