Investments (Amortized Cost and Fair Value of Fixed Maturity Holdings by Industry Type) (Details) - Corporate Debt Securities [Member] - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Corporate Securities by Investment Sector And Credit Rating [Line Items]
Amortized Cost	$ 29,203	$ 29,205
Estimated Fair Value	$ 29,494	$ 31,393
% of Total	100.00%	100.00%
Finance
Corporate Securities by Investment Sector And Credit Rating [Line Items]
Amortized Cost	$ 10,979	$ 10,896
Estimated Fair Value	$ 11,056	$ 11,653
% of Total	37.50%	37.20%
Industrial
Corporate Securities by Investment Sector And Credit Rating [Line Items]
Amortized Cost	$ 14,703	$ 14,692
Estimated Fair Value	$ 14,756	$ 15,803
% of Total	50.00%	50.30%
Utility
Corporate Securities by Investment Sector And Credit Rating [Line Items]
Amortized Cost	$ 3,521	$ 3,617
Estimated Fair Value	$ 3,682	$ 3,937
% of Total	12.50%	12.50%