Investments (Amortized Cost and Fair Value of Fixed Maturity Holdings by Industry Type) (Details) - Corporate Debt Securities [Member] - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Corporate Securities by Investment Sector And Credit Rating [Line Items]
Amortized Cost	$ 29,785	$ 29,205
Estimated Fair Value	$ 32,570	$ 31,393
% of Total	100.00%	100.00%
Financial Services Sector [Member]
Corporate Securities by Investment Sector And Credit Rating [Line Items]
Amortized Cost	$ 11,189	$ 10,896
Estimated Fair Value	$ 12,127	$ 11,653
% of Total	37.20%	37.20%
Commercial and Industrial Sector [Member]
Corporate Securities by Investment Sector And Credit Rating [Line Items]
Amortized Cost	$ 14,962	$ 14,692
Estimated Fair Value	$ 16,316	$ 15,803
% of Total	50.10%	50.30%
Utility Sector [Member]
Corporate Securities by Investment Sector And Credit Rating [Line Items]
Amortized Cost	$ 3,634	$ 3,617
Estimated Fair Value	$ 4,127	$ 3,937
% of Total	12.70%	12.50%