Investments (Fixed Maturity and Equity Securities Available-For-Sale - Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of Certain Fixed Maturity Securities
Gross Unrealized OTTI Loss	$ 13	$ 76	$ 112
Available-for-sale Securities, Debt Securities	390,442	351,402
CMBS
Summary of Certain Fixed Maturity Securities
Gross Unrealized OTTI Loss	1	1
Available-for-sale Securities, Debt Securities	12,441	12,633
Non-income producing fixed maturity securities
Summary of Certain Fixed Maturity Securities
Available-for-sale Securities, Debt Securities	44	54
Gross Unrealized Gain	$ (5)	$ 12

Amount of debt securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=65884222&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66010992&loc=d3e26610-111562

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=73527792&loc=d3e27161-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 320
-Section 50
-Paragraph 2
-Subparagraph (b)-(g)
-URI http://asc.fasb.org/extlink&oid=6957658&loc=d3e62557-112803

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant