Investments (Credit Quality Indicators For Mortgage Loans) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Mortgage Loans Credit Quality [Line Items]
Principal amount of mortgage loans on real estate	$ 7,058	$ 7,043
Percentage of total mortgage loans on real estate	100.00%	100.00%
Loan-To-Value Ratio, Less Than 65% [Member]
Mortgage Loans Credit Quality [Line Items]
Principal amount of mortgage loans on real estate	5,738	5,677
Percentage of total mortgage loans on real estate	81.30%	80.60%
Debt-service coverage ratio	1.69	1.68
Loan-To-Value Ratio, 65% To 74% [Member]
Mortgage Loans Credit Quality [Line Items]
Principal amount of mortgage loans on real estate	877	897
Percentage of total mortgage loans on real estate	12.40%	12.70%
Debt-service coverage ratio	1.39	1.39
Loan-To-Value Ratio, 75% To 100% [Member]
Mortgage Loans Credit Quality [Line Items]
Principal amount of mortgage loans on real estate	389	386
Percentage of total mortgage loans on real estate	5.50%	5.50%
Debt-service coverage ratio	0.82	0.84
Loan-To-Value Ratio, Greater Than 100% [Member]
Mortgage Loans Credit Quality [Line Items]
Principal amount of mortgage loans on real estate	$ 54	$ 83
Percentage of total mortgage loans on real estate	0.80%	1.20%
Debt-service coverage ratio	0.80	0.66