Investments (Amortized Cost and Fair Value of Fixed Maturity Holdings by Industry Type) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Corporate Secturities by Investment Sector And Credit Rating [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 29,205	$ 24,006
Available-for-sale Securities	$ 31,393	$ 23,982
Percentage Of Total Available For Sales Securities	100.00%	100.00%
Financial Services Sector [Member]
Corporate Secturities by Investment Sector And Credit Rating [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 10,896	$ 8,794
Available-for-sale Securities	$ 11,653	$ 8,731
Percentage Of Total Available For Sales Securities	37.20%	36.30%
Commercial and Industrial Sector [Member]
Corporate Secturities by Investment Sector And Credit Rating [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 14,692	$ 12,337
Available-for-sale Securities	$ 15,803	$ 12,342
Percentage Of Total Available For Sales Securities	50.30%	51.60%
Utility Industry [Member]
Corporate Secturities by Investment Sector And Credit Rating [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 3,617	$ 2,875
Available-for-sale Securities	$ 3,937	$ 2,909
Percentage Of Total Available For Sales Securities	12.50%	12.10%