Investments (Mortgage Loans - Narrative) (Details) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Mortgage Loans on Real Estate [Line Items]
Financing Receivable, Significant Purchases	$ 856	$ 1,000	$ 2,300	$ 3,200
Percentage of Mortgage Loans Classified as Performing	99.00%		99.00%		99.00%
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	0	0	0
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Provision for Loan Losses			$ 143
Commercial
Mortgage Loans on Real Estate [Line Items]
Impaired Financing Receivable, Average Recorded Investment	$ 90	$ 118	109	$ 144
Agricultural
Mortgage Loans on Real Estate [Line Items]
Impaired Financing Receivable, Average Recorded Investment	52	62	56	62
Estimated fair value of mortgage loans held-for-investment	14,600		14,600		$ 13,500
Residential
Mortgage Loans on Real Estate [Line Items]
Impaired Financing Receivable, Average Recorded Investment	202	$ 96	174	$ 72
Estimated fair value of mortgage loans held-for-investment	$ 11,400		$ 11,400		$ 9,900

The percentage of all mortgage loans that are classified as performing.

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- Definition

Amount of expense related to loan loss not accounted for as debt securities, with evidence of deterioration of credit quality.

+ References

No definition available.

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- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953682-111524

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- Definition

The amount of any significant purchases of financing receivables during the reporting period.

+ 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 (e)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

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- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5258-111524

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- Definition

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.

+ References

No definition available.

+ Details

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- Definition

Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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