Investments (Mortgage Loans - Narrative) (Details) $ in Millions	12 Months Ended
Dec. 31, 2016 USD ($) Contracts	Dec. 31, 2015 USD ($) Contracts	Dec. 31, 2014 USD ($)
Financing Receivable, Recorded Investment [Line Items]
Average Recorded Investment	$ 3	$ 3
Financing Receivable, Significant Purchases	$ 619	$ 346
Percentage of Mortgage Loans Classified as Performing	99.00%	99.00%
Financing Receivable, Modifications, Subsequent Default, Number of Contracts \| Contracts	0	0
Agricultural Portfolio Segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Average Recorded Investment	$ 3	$ 3	$ 3
Estimated fair value of mortgage loans held-for-investment	$ 1,700	$ 1,500
Loans and Leases Receivable, Number of Contract, Nonperforming, Nonaccrual of Interest \| Contracts	0	0
Financing Receivable Number of Contract of Recorded Investment Past Due \| Contracts	0	0
Commercial
Financing Receivable, Recorded Investment [Line Items]
Average Recorded Investment	$ 0	$ 0	43
Loans and Leases Receivable, Number of Contract, Nonperforming, Nonaccrual of Interest \| Contracts	0	0
Financing Receivable Number of Contract of Recorded Investment Past Due \| Contracts	0	0
Residential
Financing Receivable, Recorded Investment [Line Items]
Average Recorded Investment	$ 0	$ 0	0
Estimated fair value of mortgage loans held-for-investment	867	345
Financing Receivable, Recorded Investment, Past Due	11	11
Loans and Leases Receivable, Nonperforming, Nonaccrual of Interest	4	4
Affiliated Entity [Member]
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Significant Sales	2,300	2,000	360
Related Party Transaction, Amounts of Transaction	$ 1,600	$ 973	$ 1,000

Reflects the number of financing receivables of recorded investment that are past due at the balance sheet date.

No definition available.

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- Definition

Reflects the number of loans deemed to be questionable as to collection on which no interest is continuing to be recognized.

+ References

No definition available.

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- Definition

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

+ 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

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.

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- Definition

Recorded Investment in financing receivables that are past due at the balance sheet date.

+ 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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
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-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953401-111524

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- Definition

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

+ References

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-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
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- Definition

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

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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

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

Reflects the carrying amount of loans deemed to be questionable as to collection on which no interest is continuing to be recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Paragraph 7
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-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5111-111524

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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
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-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3)
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- Definition

Amount of transactions with related party during the financial reporting period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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