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Fair Value (Quantitative information about significant unobservable inputs in the fair value measurement of level 3 assets) (Details) - Fixed maturity securities - Income Approach Valuation Technique - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Estimated fair value	$ 136	$ 106
Minimum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Credit spread	1.00%	2.00%
Maximum
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Credit spread	12.00%	40.00%
Weighted Average
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Credit spread	3.00%	4.00%

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- Definition

fair value inputs, credit risk, counterparty

+ References

No definition available.

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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