Investments (Details 8) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	$ 147	$ 217
Interest Accrual Status of Mortgage Loans	53	29
Mortgage loans that were in non accrual status	169	237
Commercial mortgage loans portfolio segment [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	2	63
Interest Accrual Status of Mortgage Loans	0	0
Mortgage loans that were in non accrual status	84	63
Agricultural mortgage loans portfolio segment [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	116	146
Interest Accrual Status of Mortgage Loans	53	29
Mortgage loans that were in non accrual status	67	157
Residential mortgage loans portfolio segment [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	29	8
Interest Accrual Status of Mortgage Loans	0	0
Mortgage loans that were in non accrual status	$ 18	$ 17