Investments and Derivative Instruments (Details 10) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Mortgage Loans by Property Type
Mortgage Loans	$ 6,275	$ 5,728
Percent of Total	100.00%	100.00%
Agricultural [Member]
Mortgage Loans by Property Type
Mortgage Loans	198	249
Percent of Total	3.20%	4.30%
Industrial [Member]
Mortgage Loans by Property Type
Mortgage Loans	1,847	1,747
Percent of Total	29.40%	30.50%
Lodging [Member]
Mortgage Loans by Property Type
Mortgage Loans	92	93
Percent of Total	1.50%	1.60%
Multifamily [Member]
Mortgage Loans by Property Type
Mortgage Loans	1,208	1,070
Percent of Total	19.30%	18.70%
Office [Member]
Mortgage Loans by Property Type
Mortgage Loans	1,307	1,078
Percent of Total	20.80%	18.80%
Retail [Member]
Mortgage Loans by Property Type
Mortgage Loans	1,369	1,234
Percent of Total	21.80%	21.50%
Other [Member]
Mortgage Loans by Property Type
Mortgage Loans	$ 254	$ 257
Percent of Total	4.00%	4.60%