Investments (Net investment income) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net Investment Income [Line Items]
Gross investment income	$ 1,999	$ 2,181	$ 1,878
Investment expense	(64)	(63)	(61)
Net investment income	1,935	2,118	1,817
Fixed maturity securities
Net Investment Income [Line Items]
Gross investment income	1,728	1,817	1,795
Equity securities
Net Investment Income [Line Items]
Gross investment income	65	85	18
Limited partnership investments
Net Investment Income [Line Items]
Gross investment income	121	180	(22)
Mortgage loans
Net Investment Income [Line Items]
Gross investment income	57	51	50
Short term investments
Net Investment Income [Line Items]
Gross investment income	9	34	26
Trading portfolio
Net Investment Income [Line Items]
Gross investment income	18	9	7
Other
Net Investment Income [Line Items]
Gross investment income	$ 1	$ 5	$ 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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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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