Investments and Derivative Instruments (Details 8) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Commercial Mortgage Loans Credit Quality
Avg. Debt-Service Coverage Ratio	2.05
Commercial [Member]
Commercial Mortgage Loans Credit Quality
Carrying Value	$ 6,875	$ 5,728
Avg. Debt-Service Coverage Ratio	2.05	1.94
Greater than 80% [Member] | Commercial [Member]
Commercial Mortgage Loans Credit Quality
Carrying Value	566	707
Avg. Debt-Service Coverage Ratio	1.45	1.45
65% - 80% [Member] | Commercial [Member]
Commercial Mortgage Loans Credit Quality
Carrying Value	2,811	2,384
Avg. Debt-Service Coverage Ratio	1.76	1.60
Less than 65% [Member] | Commercial [Member]
Commercial Mortgage Loans Credit Quality
Carrying Value	$ 3,498	$ 2,637
Avg. Debt-Service Coverage Ratio	2.39	2.40