Investments (Past Due and Interest Accrual Status of Mortgage Loans) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	$ 141	$ 147
Interest Accrual Status of Mortgage Loans	53	53
Mortgage loans that were in non accrual status	288	169
Commercial mortgage loans portfolio segment [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	0	2
Interest Accrual Status of Mortgage Loans	0	0
Mortgage loans that were in non accrual status	204	84
Agricultural [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	103	116
Interest Accrual Status of Mortgage Loans	52	53
Mortgage loans that were in non accrual status	67	67
Residential [Member]
Past Due and Interest Accrual Status of Mortgage Loans
Past Due Status of Mortgage Loans	38	29
Interest Accrual Status of Mortgage Loans	1	0
Mortgage loans that were in non accrual status	$ 17	$ 18