Investments (Maturities of Fixed Maturity Securities) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Available-for-sale Securities, Debt Maturities [Abstract]
Amortized Cost, Due in one year or less	$ 17,822
Amortized Cost, Due after one year through five years	48,014
Amortized Cost, Due after five years through ten years	58,800
Amortized Cost, Due after ten years	121,328
Amortized Cost, Structured Securities	51,691
Amortized Cost, Subtotal	297,655	$ 286,816
Estimated Fair Value, Due in one year or less	17,960
Estimated Fair Value, Due after one year through five years	50,058
Estimated Fair Value, Due after five years through ten years	64,135
Estimated Fair Value, Due after ten years	142,131
Estimated Fair Value, Structured Securities	53,536
Debt Securities, Available-for-sale	$ 327,820	$ 298,265