Investments (Credit Quality Indicators For Commercial Mortgage Loans) (Details) - Commercial [Member] - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Mortgage Loans Credit Quality [Line Items]
Amortized Cost	$ 16,050	$ 15,511
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]
Amortized Cost	$ 14,632	$ 14,121
Percentage of total mortgage loans on real estate	91.20%	91.00%
Debt-service coverage ratio	2.39	2.35
Loan-to-value ratio, 65% to 74% [Member]
Mortgage Loans Credit Quality [Line Items]
Amortized Cost	$ 1,417	$ 1,389
Percentage of total mortgage loans on real estate	8.80%	9.00%
Debt-service coverage ratio	1.85	1.88
Loan-to-value ratio, 75% to 100% [Member]
Mortgage Loans Credit Quality [Line Items]
Amortized Cost	$ 1	$ 1
Percentage of total mortgage loans on real estate	0.00%	0.00%
Debt-service coverage ratio	0.90	1.09