Investments (Credit Quality of Agricultural and Residential Mortgage Loans) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	$ 12,669	$ 12,843
% of Total	100.00%	100.00%
Residential Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	994	958
% of Total	100.00%	100.00%
Less than 65% [Member]
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	11,676	11,908
% of Total	92.20%	92.70%
65% to 75% [Member]
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	679	590
% of Total	5.40%	4.60%
76% to 80% [Member]
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	79	92
% of Total	0.60%	0.70%
Greater than 80% [Member]
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	235	253
% of Total	1.80%	2.00%
Performing [Member]
Residential Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	967	929
% of Total	97.30%	97.00%
Nonperforming [Member]
Residential Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	$ 27	$ 29
% of Total	2.70%	3.00%