Investments (Credit Quality Indicators For Mortgage Loans) (Details) $ in Millions	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Mortgage Loans Credit Quality [Line Items]
Principal amount of mortgage loans on real estate	$ 8,678	$ 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	$ 7,718	$ 6,596
Percentage of total mortgage loans on real estate	88.90%	87.10%
Debt-service coverage ratio	2.06	1.90
Loan-to-value ratio, 65% to 74% [Member]
Mortgage Loans Credit Quality [Line Items]
Principal amount of mortgage loans on real estate	$ 653	$ 631
Percentage of total mortgage loans on real estate	7.50%	8.30%
Debt-service coverage ratio	1.60	1.55
Loan-to-value ratio, 75% to 100% [Member]
Mortgage Loans Credit Quality [Line Items]
Principal amount of mortgage loans on real estate	$ 301	$ 316
Percentage of total mortgage loans on real estate	3.50%	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	1.05	0.77