Investments (Details 35) (USD $) In Millions	Sep. 30, 2011	Dec. 31, 2010
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	$ 329	$ 296
Interest Accrual Status of Mortgage Loans	130	25
Mortgage loans that were in non accrual status	248	209
Commercial mortgage loans portfolio segment [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	155	58
Interest Accrual Status of Mortgage Loans	115	1
Mortgage loans that were in non accrual status	60	7
Agricultural mortgage loans portfolio segment [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	141	159
Interest Accrual Status of Mortgage Loans	7	13
Mortgage loans that were in non accrual status	165	177
Residential mortgage loans portfolio segment [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	33	79
Interest Accrual Status of Mortgage Loans	8	11
Mortgage loans that were in non accrual status	$ 23	$ 25