Investments (Details Textuals 6) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010 Commercial mortgage loans portfolio segment [Member]	Dec. 31, 2010 Agricultural mortgage loans portfolio segment [Member]	Dec. 31, 2010 Residential mortgage loans portfolio segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Average Investment	$ 681	$ 588	$ 192	$ 284	$ 16
Interest Income Recognized - Cash Basis			$ 6	$ 8	$ 0

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

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=7512638&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=7512638&loc=d3e5258-111524

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration