Investments (Details Textuals 16) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Agricultural mortgage loans portfolio segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Estimated fair value of mortgage loans held-for-investment	$ 13,400	$ 13,600
Residential mortgage loans portfolio segment [Member]
Financing Receivable, Recorded Investment [Line Items]
Estimated fair value of mortgage loans held-for-investment	$ 802	$ 737

The amount of the recorded 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, accounts receivable (with terms exceeding one year), notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Receivable

-URI http://asc.fasb.org/extlink&oid=6953735

Name:	us-gaap_FinancingReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant