Investments and Derivative Instruments (Details 8) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Commercial Mortgage Loans Credit Quality
Avg. Debt-Service	2.13
Commercial [Member]
Commercial Mortgage Loans Credit Quality
Carrying Value	$ 3,585	$ 4,935
Avg. Debt-Service	2.13	2.34
Greater than 80% [Member] | Commercial [Member]
Commercial Mortgage Loans Credit Quality
Carrying Value	108	137
Avg. Debt-Service	1.00	0.89
65% - 80% [Member] | Commercial [Member]
Commercial Mortgage Loans Credit Quality
Carrying Value	1,063	1,717
Avg. Debt-Service	2.04	2.27
Less than 65% [Member] | Commercial [Member]
Commercial Mortgage Loans Credit Quality
Carrying Value	$ 2,414	$ 3,081
Avg. Debt-Service	2.23	2.44