Investments (Credit Quality Indicators For Mortgage Loans) (Details) $ in Millions	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Mortgage Loans Credit Quality [Line Items]
Carrying value of mortgage loans on real estate	$ 9,889	$ 8,678
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]
Carrying value of mortgage loans on real estate	$ 8,709	$ 7,718
Percentage of total mortgage loans on real estate	88.00%	88.90%
Debt-service coverage ratio	2.16	2.06
Loan-to-value ratio, 65% to 74% [Member]
Mortgage Loans Credit Quality [Line Items]
Carrying value of mortgage loans on real estate	$ 1,009	$ 653
Percentage of total mortgage loans on real estate	10.20%	7.50%
Debt-service coverage ratio	1.87	1.60
Loan-to-value ratio, 75% to 100% [Member]
Mortgage Loans Credit Quality [Line Items]
Carrying value of mortgage loans on real estate	$ 166	$ 301
Percentage of total mortgage loans on real estate	1.70%	3.50%
Debt-service coverage ratio	0.82	0.83
Loan-To-Value Ratio, Greater Than 100% [Member]
Mortgage Loans Credit Quality [Line Items]
Carrying value of mortgage loans on real estate	$ 5	$ 6
Percentage of total mortgage loans on real estate	0.10%	0.10%
Debt-service coverage ratio	1.04	1.05