Investments and Derivative Instruments (Details 10) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Mortgage Loans by Property Type
Mortgage loans, carrying value	$ 3,585	$ 4,935
Percent of Total	100.00%	100.00%
Agricultural [Member]
Mortgage Loans by Property Type
Mortgage loans, carrying value	96	109
Percent of Total	2.70%	2.20%
Industrial [Member]
Mortgage Loans by Property Type
Mortgage loans, carrying value	1,143	1,519
Percent of Total	31.90%	30.80%
Lodging [Member]
Mortgage Loans by Property Type
Mortgage loans, carrying value	60	81
Percent of Total	1.70%	1.60%
Multifamily [Member]
Mortgage Loans by Property Type
Mortgage loans, carrying value	586	869
Percent of Total	16.30%	17.60%
Office [Member]
Mortgage Loans by Property Type
Mortgage loans, carrying value	779	1,120
Percent of Total	21.70%	22.70%
Retail [Member]
Mortgage Loans by Property Type
Mortgage loans, carrying value	827	1,047
Percent of Total	23.10%	21.20%
Other [Member]
Mortgage Loans by Property Type
Mortgage loans, carrying value	$ 94	$ 190
Percent of Total	2.60%	3.90%