Investments (Details 45) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Variable Interest Entity [Line Items]
Total Assets	$ 12,933	$ 12,581
Total Liabilities	13,507	13,265
Other limited partnership interests [Member]
Variable Interest Entity [Line Items]
Total Assets	1,409	1,302
Total Liabilities	1,980	1,982
Real estate joint ventures [Member]
Variable Interest Entity [Line Items]
Total Assets	18	22
Total Liabilities	21	26
RMBS [Member]
Variable Interest Entity [Line Items]
Total Assets	6,154	6,494
Total Liabilities	6,154	6,494
CMBS [Member]
Variable Interest Entity [Line Items]
Total Assets	2,461	2,227
Total Liabilities	2,461	2,227
ABS [Member]
Variable Interest Entity [Line Items]
Total Assets	2,276	1,878
Total Liabilities	2,276	1,878
U.S. corporate securities [Member]
Variable Interest Entity [Line Items]
Total Assets	355	424
Total Liabilities	355	424
Foreign corporate securities [Member]
Variable Interest Entity [Line Items]
Total Assets	260	234
Total Liabilities	$ 260	$ 234