Investments (Details 34) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	$ 12,600	$ 13,129
% of Total	100.00%	100.00%
Residential Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	818	689
% of Total	100.00%	100.00%
Less than 65% [Member]
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	11,651	11,802
% of Total	92.50%	89.90%
65% to 75% [Member]
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	658	874
% of Total	5.20%	6.70%
76% to 80% [Member]
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	35	76
% of Total	0.30%	0.60%
Greater than 80% [Member]
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	256	377
% of Total	2.00%	2.80%
Performing [Member]
Residential Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	792	671
% of Total	96.80%	97.40%
Nonperforming [Member]
Residential Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	$ 26	$ 18
% of Total	3.20%	2.60%