| **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** | Jun. 30, 2017 | Dec. 31, 2016 |
|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                                                                                                |          |          |
| Estimated Fair Value (In millions)                                                                                                                                                                                                  | $ 125         | $ 106         |
| Minimum                                                                                                                                                                                                                             |          |          |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                                                                                                |          |          |
| Credit spread                                                                                                                                                                                                                       | 2.00%         | 2.00%         |
| Maximum                                                                                                                                                                                                                             |          |          |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                                                                                                |          |          |
| Credit spread                                                                                                                                                                                                                       | 40.00%        | 40.00%        |
| Weighted Average                                                                                                                                                                                                                    |          |          |
| **Fair Value Inputs, Assets, Quantitative Information [Line Items]**                                                                                                                                                                |          |          |
| Credit spread                                                                                                                                                                                                                       | 4.00%         | 4.00%         |

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| - Definition
fair value inputs, credit risk, counterparty
+ References
No definition available.
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| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   |
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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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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - 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.
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