Investments (Credit Quality of Agricultural and Residential Mortgage Loans) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 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	1,741	958
% of Total	100.00%	100.00%
Less than 65% [Member]
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	11,631	11,908
% of Total	91.80%	92.70%
65% to 75% [Member]
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	842	590
% of Total	6.60%	4.60%
76% to 80% [Member]
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	73	92
% of Total	0.60%	0.70%
Greater than 80% [Member]
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	123	253
% of Total	1.00%	2.00%
Performing [Member]
Residential Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	1,703	929
% of Total	97.80%	97.00%
Nonperforming [Member]
Residential Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	$ 38	$ 29
% of Total	2.20%	3.00%