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	$ 1,300	$ 1,260
% of Total	100.00%	100.00%
Less than 65% [Member]
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	1,210	1,184
% of Total	93.10%	94.00%
65% to 75% [Member]
Agricultural Mortgage Loans - by Credit Quality Indicator:
Recorded investment in Mortgage Loan	$ 90	$ 76
% of Total	6.90%	6.00%