Investments and Derivative Instruments (Details 8) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Commercial Mortgage Loans Credit Quality
Avg. Debt-Service Coverage Ratio	1.95
Commercial [Member]
Commercial Mortgage Loans Credit Quality
Carrying Value	$ 6,275	$ 5,728
Avg. Debt-Service Coverage Ratio	1.95	1.94
Greater than 80% [Member] | Commercial [Member]
Commercial Mortgage Loans Credit Quality
Carrying Value	636	707
Avg. Debt-Service Coverage Ratio	1.34	1.45
65% - 80% [Member] | Commercial [Member]
Commercial Mortgage Loans Credit Quality
Carrying Value	2,782	2,384
Avg. Debt-Service Coverage Ratio	1.61	1.60
Less than 65% [Member] | Commercial [Member]
Commercial Mortgage Loans Credit Quality
Carrying Value	$ 2,857	$ 2,637
Avg. Debt-Service Coverage Ratio	2.44	2.40