Investments (Credit Quality Indicators For Commercial Mortgage Loans) (Details) - Commercial [Member] $ in Millions	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Mortgage Loans Credit Quality [Line Items]
Carrying value of mortgage loans on real estate	$ 13,582	$ 13,012
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	$ 12,368	$ 11,716
Percentage of total mortgage loans on real estate	91.10%	90.10%
Debt-service coverage ratio	2.27	2.30
Loan-to-value ratio, 65% to 74% [Member]
Mortgage Loans Credit Quality [Line Items]
Carrying value of mortgage loans on real estate	$ 1,175	$ 1,238
Percentage of total mortgage loans on real estate	8.60%	9.50%
Debt-service coverage ratio	1.74	1.76
Loan-to-value ratio, 75% to 100% [Member]
Mortgage Loans Credit Quality [Line Items]
Carrying value of mortgage loans on real estate	$ 39	$ 58
Percentage of total mortgage loans on real estate	0.30%	0.40%
Debt-service coverage ratio	1.20	0.95