Commitments and Contingencies - Restricted Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Loss Contingencies [Line Items]
Fixed maturity collateral pledged to FHLB	$ 602	$ 405
FHLB restricted stock	67	33
Other fixed maturities-state deposits	175	197
Securities pledged	2,087	1,409
Total restricted assets	2,931	2,044
Securities pledged as collateral
Loss Contingencies [Line Items]
Fair value of loaned securities	1,854	1,133
Fair value of securities delivered as collateral	233	276
Line of Credit \| Federal Home Loan Bank Borrowings
Loss Contingencies [Line Items]
Fixed maturity collateral pledged to FHLB	602	405
Line of Credit Facility, Fair Value of Amount Outstanding	$ 501	$ 300

The fair value of available-for-sale securities that serve as collateral for borrowings.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
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Fair value portion of investments in Federal Home Loan Bank (FHLBank) stock.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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Fair value of the amount outstanding under the credit facility.

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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.

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For an unclassified balance sheet, this item represents investments in debt securities having predetermined or determinable maturity dates.

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The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for FHLB debt obligations, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

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Investments which are not defined as or included in marketable (debt, equity, or other) securities whose use is restricted in whole or in part, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet.

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Fair value of the securities pledged as collateral against securities loaned.

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Fair value of financial instrument held by the entity for its own account (proprietary securities) for trading or investment purposes that are carried at fair value and pledged to counterparties as collateral for financing transactions.

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