Insurance (Guarantees Related to Universal and Variable Life Contracts) (Details) - Secondary Guarantees - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Universal Life
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (3)	$ 6,133	$ 6,244
Net amount at risk	$ 73,680	$ 75,304
Average attained age of policyholders	65 years	64 years
Variable Life
Net Amount at Risk by Product and Guarantee [Line Items]
Total account value (3)	$ 1,068	$ 1,021
Net amount at risk	$ 13,156	$ 13,848
Average attained age of policyholders	44 years	44 years

Value of the separate and general accounts corresponding to the specified product, guarantee type and subset of the guarantee.

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Net amount at risk, representing the guaranteed benefit in excess of the current account balance corresponding to the specified product, guarantee type and subset of the guarantee.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 80
-Section 50
-Paragraph 1
-Subparagraph (d)(3),(5)
-URI http://asc.fasb.org/extlink&oid=6484115&loc=d3e19393-158473

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=6588021&loc=d3e7104-158389

+ Details

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Period Type:	instant

- Definition

Weighted average attained age of policyholders or contract holders in the specified guarantee type and subset of guarantee class, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 80
-Section 50
-Paragraph 1
-Subparagraph ((d)(5))
-URI http://asc.fasb.org/extlink&oid=6484115&loc=d3e19393-158473

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 20
-Section 55
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=6588021&loc=d3e7104-158389

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- Details

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- Details

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- Details

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