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]
Less: Investment expenses	$ 196	$ 178	$ 176
Net investment income	3,338	3,078	3,207
Fixed Maturity Securities
Net Investment Income [Line Items]
Gross Investment Income, Operating	2,565	2,420	2,642
Equity securities
Net Investment Income [Line Items]
Gross Investment Income, Operating	7	9	14
Mortgage loans
Net Investment Income [Line Items]
Gross Investment Income, Operating	543	454	413
Policy loans
Net Investment Income [Line Items]
Gross Investment Income, Operating	85	73	78
Real estate joint ventures
Net Investment Income [Line Items]
Gross Investment Income, Operating	47	53	32
Other limited partnership interests
Net Investment Income [Line Items]
Gross Investment Income, Operating	211	184	163
Cash, cash equivalents and short-term investments
Net Investment Income [Line Items]
Gross Investment Income, Operating	35	35	20
Other investments
Net Investment Income [Line Items]
Gross Investment Income, Operating	41	28	21
Securities Investment
Net Investment Income [Line Items]
Gross Investment Income, Operating	$ 3,534	$ 3,256	$ 3,383

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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-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
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-Section S99
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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

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