Investments and Derivative Instruments (Details 10) (USD $) In Millions, unless otherwise specified	Jun. 30, 2011	Dec. 31, 2010
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	$ 5,304	$ 4,489
Percent of Total	100.00%	100.00%
Agricultural [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	258	315
Percent of Total	4.90%	7.00%
Industrial [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	1,615	1,141
Percent of Total	30.50%	25.40%
Lodging [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	124	132
Percent of Total	2.30%	2.90%
Multifamily [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	974	713
Percent of Total	18.40%	15.90%
Office [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	944	986
Percent of Total	17.80%	22.10%
Retail [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	986	669
Percent of Total	18.60%	14.90%
Other [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	294	384
Percent of Total	5.40%	8.50%
Residential [Member]
Schedule of Available-for-sale Securities Mortgage Loans [Line Items]
Carrying Value	$ 109	$ 149
Percent of Total	2.10%	3.30%