Investments (Mortgage Loans - Narrative) (Details) (USD $)	3 Months Ended
Mar. 31, 2013 Contracts	Mar. 31, 2012 Contracts	Dec. 31, 2012
Financing Receivable, Recorded Investment [Line Items]
Financing Receivable, Significant Purchases	$ 50,000,000	$ 0
Percentage of Mortgage Loans Classified as Performing	99.00%		99.00%
Number of Mortgage Loans	0	0
Agricultural [Member]
Financing Receivable, Recorded Investment [Line Items]
Estimated fair value of mortgage loans held-for-investment	13,100,000,000		13,300,000,000
Number of Mortgage Loans	0	1
Carrying Value after Specific Valuation Allowance	0	8,000,000
Residential [Member]
Financing Receivable, Recorded Investment [Line Items]
Estimated fair value of mortgage loans held-for-investment	$ 1,000,000,000		1,000,000,000

Financing receivable modifications number of contracts.

No definition available.

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- Definition

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

+ References

No definition available.

+ Details

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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=7512638&loc=SL6953682-111524

+ Details

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- Definition

Amount of investment related to financing receivables modified by troubled debt restructurings within the previous 12 months, for which there was a payment default.

+ References

+ Details

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- Details

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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=7512638&loc=SL6953423-111524

+ 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

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 3

-Article 5

+ Details

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