Investments (Net Investment Income) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Investment Income [Line Items]
Gross Investment Income, Operating	$ 2,965	$ 3,100	$ 2,985
Less: Investment expenses	175	173	126
Net investment income	2,973	3,111	3,001
Securities Investment
Net Investment Income [Line Items]
Gross Investment Income, Operating	3,140	3,273	3,111
Fixed maturity securities
Net Investment Income [Line Items]
Gross Investment Income, Operating	2,347	2,567	2,398
Equity securities
Net Investment Income [Line Items]
Gross Investment Income, Operating	12	19	19
Mortgage loans
Net Investment Income [Line Items]
Gross Investment Income, Operating	442	393	367
Policy loans
Net Investment Income [Line Items]
Gross Investment Income, Operating	49	54	54
Real estate and real estate joint ventures
Net Investment Income [Line Items]
Gross Investment Income, Operating	53	32	108
Other limited partnership interests
Net Investment Income [Line Items]
Gross Investment Income, Operating	182	163	134
Cash, cash equivalents and short-term investments
Net Investment Income [Line Items]
Gross Investment Income, Operating	30	20	9
Other investments
Net Investment Income [Line Items]
Gross Investment Income, Operating	25	25	22
FVO CSEs — interest income — commercial mortgage loans \| Consolidated Securitization Entities
Net Investment Income [Line Items]
Gross Investment Income, Operating	$ 8	$ 11	$ 16

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.

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Amount of expenses related to the generation of investment income.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.9)
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04.2)
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

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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/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(2))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 235
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-16(Column G))
-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574960-122915

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No definition available.

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