Investments (Securities Lending - Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Amortized cost
Securities Financing Transaction [Line Items]
Securities Loaned	$ 26,599	$ 27,223
Estimated fair value
Securities Financing Transaction [Line Items]
Securities Loaned	30,474	$ 29,646
Reserve for Off-balance Sheet Activities \| Amortized cost
Securities Financing Transaction [Line Items]
Securities Loaned	105
Reserve for Off-balance Sheet Activities \| Estimated fair value
Securities Financing Transaction [Line Items]
Securities Loaned	$ 105

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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 405
-Section 55
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=35710563&loc=d3e44140-110984

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=51825145&loc=SL20226008-175313

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=55761124&loc=SL6224234-111729

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant