Investments (Securities Lending) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 19,244	$ 19,417
Security collateral on deposit from counterparties	47	19
Reinvestment portfolio — estimated fair value	19,374	19,508
Amortized cost
Securities Financing Transaction [Line Items]
Securities loaned	18,052	17,801
Estimated fair value
Securities Financing Transaction [Line Items]
Securities loaned	$ 18,846	$ 19,028

This element represents the estimated fair value of the securities lending reinvestment portfolio.

No definition available.

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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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- Definition

Amount, after the effects of master netting arrangements, of securities loaned to entities in exchange for collateral. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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- Definition

The carrying value as of the balance sheet date of the assets received as collateral against securities loaned to other broker-dealers. Borrowers of securities generally are required to provide collateral to the lenders of securities, commonly cash but sometimes other securities or standby letters of credit, with a value slightly higher than that of the securities borrowed. In instances where the entity is permitted to sell or re-pledge these securities, the entity reports the fair value of the collateral received and the related obligation to return the collateral as a liability.

+ References

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- Definition

Carrying amount of liabilities associated with financial assets accounted for as secured borrowings recognized in the transferor's statement of financial position at the end of each period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(ii)
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