Investments (Credit Quality Indicators For Mortgage Loans) (Details) $ in Millions	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Mortgage Loans Credit Quality [Line Items]
Carrying value of mortgage loans on real estate	$ 12,561	$ 10,762
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	$ 11,297	$ 9,642
Percentage of total mortgage loans on real estate	89.90%	89.60%
Debt-service coverage ratio	2.30	2.26
Loan-to-value ratio, 65% to 74% [Member]
Mortgage Loans Credit Quality [Line Items]
Carrying value of mortgage loans on real estate	$ 1,187	$ 1,000
Percentage of total mortgage loans on real estate	9.50%	9.30%
Debt-service coverage ratio	1.79	1.94
Loan-to-value ratio, 75% to 100% [Member]
Mortgage Loans Credit Quality [Line Items]
Carrying value of mortgage loans on real estate	$ 74	$ 112
Percentage of total mortgage loans on real estate	0.60%	1.00%
Debt-service coverage ratio	0.95	0.97
Loan-To-Value Ratio, Greater Than 100% [Member]
Mortgage Loans Credit Quality [Line Items]
Carrying value of mortgage loans on real estate	$ 3	$ 8
Percentage of total mortgage loans on real estate	0.00%	0.10%
Debt-service coverage ratio	0.21	0.82