Investments Narrative (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Investment Text Details [Abstract]
Investments supporting run-off settlement annuity business	$ 3,000,000,000	$ 3,100,000,000
Gross unrealized appreciation of investments supporting run-off settlement annuity business	816,000,000	883,000,000
Gross unrealized depreciation of investments supporting run-off settlement annuity business	6,000,000	8,000,000
Corporate Securities Included In Short Term Investments	1,900,000,000	1,100,000,000
Federal Government Securities Included In Short Term Investments	189,000,000	167,000,000
Money Market Funds Included In Short Term Investments	67,000,000	217,000,000
Trading and hybrid securities excluded from gross unrealized appreciation	16,000,000	16,000,000
Financing Receivables Credit Quality Text Details [Abstract]
Financing Receivable Credit Quality Debt Service Coverage	1.55	1.56
Financing Receivable Credit Quality Loan To Value Ratio	65.00%	65.00%
Problem And Potential Problem Mortgage Loans	215,000,000	215,000,000
Average Recorded Investment Impaired Commercial Mortgage Loans	132,000,000		201,000,000
Mortgage Loans Restructured		119,000,000
Modified Loans Note 1		100,000,000
Modified Loans Note 2		19,000,000
Paydown Of Modified Loan Note 1		46,000,000
Remaining Amount Of Modified Loan Note 1 Reclassified To Good Standing		$ 54,000,000