Investments (Credit Quality Indicators) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Financing Percentage	86.00%
Loan To Value Ratio Percent Of Investment Less Than Eighty Percent [Member]
Financing Receivable	$ 399	$ 384
Financing Percentage		85.00%
Debt Service Coverage Ratio, Less Than One Point Zero X [Member] | Loan-to-Value Ratio Greater than Hundred Percent [Member]
Financing Receivable	$ 59	$ 19
Financing Percentage	13.00%	4.00%
Debt Service Coverage Ratio Percent Of Investment One Point Zero X Or Greater [Member]
Financing Percentage	87.00%	96.00%