Investments (Credit Quality Indicators) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Loan To Value Ratio Percent Of Investment Less Than Eighty Percent [Member]
Financing Receivable	$ 363	$ 384
Financing Percentage	85.00%	85.00%
Debt Service Coverage Ratio, Less Than One Point Zero X [Member] \| Loan-to-Value Ratio Greater than Hundred Percent [Member]
Financing Receivable	$ 17	$ 19
Financing Percentage	4.00%	4.00%
Debt Service Coverage Ratio Percent Of Investment One Point Zero X Or Greater [Member]
Financing Percentage	96.00%	96.00%

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.

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

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