Investments (Repurchase Agreements - Securities Lending) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 26,440	$ 26,755
Reinvestment portfolio — estimated fair value	26,652	26,704
Repurchase Agreements [Member]
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	1,951	102
Reinvestment portfolio — estimated fair value	1,963	100
Repurchase Agreements [Member] \| Amortized cost
Securities Financing Transaction [Line Items]
Securities Sold under Agreements to Repurchase	1,836	98
Repurchase Agreements [Member] \| Estimated fair value
Securities Financing Transaction [Line Items]
Securities Sold under Agreements to Repurchase	$ 1,982	$ 113

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.

+ Details

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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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
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-Section S99
-Paragraph 1
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13(1))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=49176635&loc=d3e9760-107771

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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/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
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-Paragraph 1A
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+ Details

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