Investments (Concentrations of Credit Risk - Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	$ 564
Securities holdings exposure in single issuer greater than stated percentage of Company's equity	10.00%	10.00%
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 300	$ 0
Foreign government \| Japan
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Government and agency fixed maturity securities	27,500	$ 24,700
Foreign government \| KOREA, REPUBLIC OF
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Securities holdings exposure in single issuer greater than stated percentage of Company's equity		10.00%
Government and agency fixed maturity securities	6,500
U.S. government and agency
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	300
Investment in Federal Home Loan Bank Stock [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	$ 12
Securities Investment [Member] \| Securities Financing Transaction, Fair Value [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Percentage of Reinvestment Portfolio in Fixed Maturity Securities	59.00%
Repurchase Agreements [Member] \| Securities Financing Transaction, Fair Value [Member]
Fair Value, Concentration of Risk, Financial Statement Captions [Line Items]
Percentage of Reinvestment Portfolio in Fixed Maturity Securities	63.00%

The percentage of the reinvestment portfolio acquired with the cash collateral consists mainly of Fixed maturities.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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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

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- Definition

Amount of advances from the Federal Home Loan Bank (FHLB).

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- Definition

Amount of the collateral pledged in support of federal home loan bank advances outstanding.

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