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	$ 11	$ 45
Recorded Investment	10	44
Valuation Allowances	1	3
Unpaid Principal Balance	304	220
Recorded Investment	280	209
Recorded Investment	64,615	59,292
Valuation Allowances	303	278
Carrying Value	289	250
Average Recorded Investment	327	271
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	41,500	38,440
Valuation Allowances	202	188
Carrying Value	12	57
Average Recorded Investment	90	127	$ 316
Agricultural
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	11	45
Recorded Investment	10	44
Valuation Allowances	1	3
Unpaid Principal Balance	27	22
Recorded Investment	27	21
Recorded Investment	12,527	11,584
Valuation Allowances	38	34
Carrying Value	36	62
Average Recorded Investment	49	60	77
Residential
Mortgage Loans on Real Estate [Line Items]
Unpaid Principal Balance	0	0
Recorded Investment	0	0
Valuation Allowances	0	0
Unpaid Principal Balance	265	141
Recorded Investment	241	131
Recorded Investment	10,588	9,268
Valuation Allowances	63	56
Carrying Value	241	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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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)
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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 (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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-Section 50
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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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+ References

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
-Publisher FASB
-Name Accounting Standards Codification
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