Investments (Repurchase Agreements - 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
Reinvestment portfolio — estimated fair value	19,374	19,508
Repurchase Agreements [Member]
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	2,560	1,102
Reinvestment portfolio — estimated fair value	2,568	1,102
Repurchase Agreements [Member] \| Amortized cost
Securities Financing Transaction [Line Items]
Securities Sold under Agreements to Repurchase	2,519	994
Repurchase Agreements [Member] \| Estimated fair value
Securities Financing Transaction [Line Items]
Securities Sold under Agreements to Repurchase	$ 2,622	$ 1,141

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 funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

+ 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
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