Investments (Credit Quality Indicators For Mortgage Loans) (Details) $ in Millions	Sep. 30, 2015 USD ($)	Dec. 31, 2014 USD ($)
Mortgage Loans Credit Quality [Line Items]
Principal amount of mortgage loans on real estate	$ 8,431	$ 7,574
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	$ 7,432	$ 6,596
Percentage of total mortgage loans on real estate	88.10%	87.10%
Debt-service coverage ratio	2.05	1.90
Loan-To-Value Ratio, 65% To 74% [Member]
Mortgage Loans Credit Quality [Line Items]
Principal amount of mortgage loans on real estate	$ 655	$ 631
Percentage of total mortgage loans on real estate	7.80%	8.30%
Debt-service coverage ratio	1.61	1.55
Loan-To-Value Ratio, 75% To 100% [Member]
Mortgage Loans Credit Quality [Line Items]
Principal amount of mortgage loans on real estate	$ 338	$ 316
Percentage of total mortgage loans on real estate	4.00%	4.20%
Debt-service coverage ratio	0.83	0.77
Loan-To-Value Ratio, Greater Than 100% [Member]
Mortgage Loans Credit Quality [Line Items]
Principal amount of mortgage loans on real estate	$ 6	$ 31
Percentage of total mortgage loans on real estate	0.10%	0.40%
Debt-service coverage ratio	1.03	0.77