Investments (Details 35) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	$ 195	$ 217
Interest Accrual Status of Mortgage Loans	55	29
Mortgage loans that were in non accrual status	288	237
Commercial mortgage loans portfolio segment [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	81	63
Interest Accrual Status of Mortgage Loans	0	0
Mortgage loans that were in non accrual status	193	63
Agricultural mortgage loans portfolio segment [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	88	146
Interest Accrual Status of Mortgage Loans	55	29
Mortgage loans that were in non accrual status	69	157
Residential mortgage loans portfolio segment [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	26	8
Interest Accrual Status of Mortgage Loans	0	0
Mortgage loans that were in non accrual status	$ 26	$ 17