Investments (Maturities of Fixed Maturity Securities) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Available-for-sale Securities, Debt Maturities [Abstract]
Amortized Cost, Due in one year or less	$ 16,336
Amortized Cost, Due after one year through five years	51,147
Amortized Cost, Due after five years through ten years	57,849
Amortized Cost, Due after ten years	114,949
Amortized Cost, Structured Securities	50,948
Amortized Cost, Subtotal	291,229	$ 286,816
Estimated Fair Value, Due in one year or less	16,415
Estimated Fair Value, Due after one year through five years	53,234
Estimated Fair Value, Due after five years through ten years	62,407
Estimated Fair Value, Due after ten years	133,866
Estimated Fair Value, Structured Securities	52,767
Estimated Fair Value of Fixed Maturity Securities AFS	$ 318,689	$ 298,265