Investments (Mortgage Loans and Valuation Allowance by Portfolio Segment) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	$ 15	$ 49
Recorded Investment	13	47
Valuation Allowances	1	3
Unpaid Principal Balance	305	220
Recorded Investment	281	209
Recorded Investment	73,893	66,678
Valuation Allowances	343	315
Carrying Value	293	253
Average Recorded Investment	330	274
Commercial
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Valuation Allowances	0	0
Unpaid Principal Balance	12	57
Recorded Investment	12	57
Recorded Investment	48,023	43,955
Valuation Allowances	234	217
Carrying Value	12	57
Average Recorded Investment	90	127	$ 359
Agricultural
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	15	49
Recorded Investment	13	47
Valuation Allowances	1	3
Unpaid Principal Balance	27	22
Recorded Investment	27	21
Recorded Investment	14,416	13,120
Valuation Allowances	43	39
Carrying Value	39	65
Average Recorded Investment	52	63	80
Residential
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Valuation Allowances	0	0
Unpaid Principal Balance	266	141
Recorded Investment	242	131
Recorded Investment	11,454	9,603
Valuation Allowances	66	59
Carrying Value	242	131
Average Recorded Investment	$ 188	$ 84	$ 19

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=66008989&loc=SL6953423-111524

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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