Investments (Details 35) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	$ 145	$ 217
Interest Accrual Status of Mortgage Loans	47	29
Mortgage loans that were in non accrual status	111	237
Commercial mortgage loans portfolio segment [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	0	63
Interest Accrual Status of Mortgage Loans	0	0
Mortgage loans that were in non accrual status	0	63
Agricultural mortgage loans portfolio segment [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	139	146
Interest Accrual Status of Mortgage Loans	47	29
Mortgage loans that were in non accrual status	95	157
Residential mortgage loans portfolio segment [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	6	8
Interest Accrual Status of Mortgage Loans	0	0
Mortgage loans that were in non accrual status	$ 16	$ 17