Reinsurance (Effect of Reinsurance on Life Insurance In Force) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reinsurance Disclosures [Abstract]
Reinsurance Premiums for Insurance Companies, by Product Segment, Gross Amount	$ 1,462	$ 1,576	$ 1,686
Reinsurance Premiums for Insurance Companies, by Product Segment, Amount Assumed from Other Companies	3,297,275	3,062,525	2,995,079
Reinsurance Premiums for Insurance Companies, by Product Segment, Amount Ceded to Other Companies	205,529	214,727	222,388
Reinsurance Premiums for Insurance Companies, by Product Segment, Net Amount	$ 3,093,208	$ 2,849,374	$ 2,774,377
Reinsurance Premiums for Insurance Companies, by Product Segment, Percentage of Amount Assumed to Net	106.60%	107.50%	108.00%

Amount of life insurance issued and outstanding assumed from other entities. Includes, but not limited to, dividends and adjustments to face value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 235
-Section S99
-Paragraph 2
-Subparagraph (SX 210.12-17)
-URI http://asc.fasb.org/extlink&oid=34713774&loc=d3e574992-122915

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- Definition

Amount of life insurance issued and outstanding ceded to other entities. Includes, but not limited to, dividends and adjustments to face value.

+ References

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- Definition

Amount before contracts ceded to other entities and contracts assumed by the entity of life insurance issued and outstanding. Includes, but not limited to, dividends and adjustments to face value.

+ References

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- Definition

Amount after contracts ceded to other entities and contracts assumed by the entity of life insurance issued and outstanding. Includes, but not limited to, dividends and adjustments to face value.

+ References

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- Definition

Percentage of assumed life insurance issued and outstanding contracts to life insurance issued and outstanding after contracts ceded to other entities and contracts assumed by the entity. Includes, but not limited to, dividends and adjustments to face value.

+ References

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- References

No definition available.

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