Investments (Amortized Cost and Fair Value of Fixed Maturity Holdings by Industry Type) (Details) - Corporate Debt Securities [Member] - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Corporate Securities by Investment Sector And Credit Rating [Line Items]
Amortized Cost	$ 31,044	$ 29,205
Estimated Fair Value	$ 34,259	$ 31,393
% of Total	100.00%	100.00%
Financial Services Sector [Member]
Corporate Securities by Investment Sector And Credit Rating [Line Items]
Amortized Cost	$ 11,550	$ 10,896
Estimated Fair Value	$ 12,658	$ 11,653
% of Total	37.00%	37.20%
Commercial and Industrial Sector [Member]
Corporate Securities by Investment Sector And Credit Rating [Line Items]
Amortized Cost	$ 15,709	$ 14,692
Estimated Fair Value	$ 17,280	$ 15,803
% of Total	50.40%	50.30%
Utility Sector [Member]
Corporate Securities by Investment Sector And Credit Rating [Line Items]
Amortized Cost	$ 3,785	$ 3,617
Estimated Fair Value	$ 4,321	$ 3,937
% of Total	12.60%	12.50%