Investment Holding Level 4 Concentration of Credit Risk (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Concentration Risk [Line Items]
Fair Value, Concentration of Risk, Investments	$ 0	$ 0
Concentration Risk, Benchmark Description	greater than 10% of the Company's stockholder's equity	greater than 10% of the Company's stockholder's equity
HSBC Holding plc. [Member] \| Corporate Debt Securities [Member]
Concentration Risk [Line Items]
Largest Exposure by Issuer, Percent of Invested Assets	1.00%
Oracle Corp [Member] \| Corporate Debt Securities [Member]
Concentration Risk [Line Items]
Largest Exposure by Issuer, Percent of Invested Assets	1.00%
National Grid plc, [Member] \| Corporate Debt Securities [Member]
Concentration Risk [Line Items]
Largest Exposure by Issuer, Percent of Invested Assets	1.00%
Verizon Communications Inc. [Member] \| Corporate Debt Securities [Member]
Concentration Risk [Line Items]
Largest Exposure by Issuer, Percent of Invested Assets		1.00%
Morgan Stanley [Member] \| Corporate Debt Securities [Member]
Concentration Risk [Line Items]
Largest Exposure by Issuer, Percent of Invested Assets		1.00%
BANK OF AMERICA - MERRILL LYNCH INSTINCT X ATS [Member] \| Corporate Debt Securities [Member]
Concentration Risk [Line Items]
Largest Exposure by Issuer, Percent of Invested Assets		1.00%
Financial Services [Member] \| Corporate Debt Securities [Member]
Concentration Risk [Line Items]
Largest Exposure by Sector, Percent of Invested Assets	9.00%	10.00%
Consumer Non-cyclical [Member] \| Corporate Debt Securities [Member]
Concentration Risk [Line Items]
Largest Exposure by Sector, Percent of Invested Assets	7.00%	7.00%
Public Utility, Bonds [Member] \| Corporate Debt Securities [Member]
Concentration Risk [Line Items]
Largest Exposure by Sector, Percent of Invested Assets	9.00%	9.00%

The percent of invested assets by the Company's largest exposure by issuer.

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The percent of invested assets by the Company's largest exposure by sector.

+ References

No definition available.

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Identifies or describes the benchmark that serves as the denominator in the calculation of the percentage of concentration risk.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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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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This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
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