Investments (Mortgage Loans and Valuation Allowance by Portfolio Segment) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	$ 22	$ 11
Recorded Investment	21	10
Valuation Allowances	2	1
Unpaid Principal Balance	363	304
Recorded Investment	332	280
Recorded Investment	67,456	64,615
Valuation Allowances	314	303
Carrying Value	351	289
Commercial
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Valuation Allowances	0	0
Unpaid Principal Balance	0	12
Recorded Investment	0	12
Recorded Investment	43,243	41,500
Valuation Allowances	213	202
Carrying Value	0	12
Agricultural
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	22	11
Recorded Investment	21	10
Valuation Allowances	2	1
Unpaid Principal Balance	28	27
Recorded Investment	28	27
Recorded Investment	12,918	12,527
Valuation Allowances	39	38
Carrying Value	47	36
Residential
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Valuation Allowances	0	0
Unpaid Principal Balance	335	265
Recorded Investment	304	241
Recorded Investment	11,295	10,588
Valuation Allowances	62	63
Carrying Value	$ 304	$ 241

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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The balance of financing receivables that were collectively evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953550-111524

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
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-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

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+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 15
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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.

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