Investments (Maturities of Fixed Maturity Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Available-for-sale Securities, Debt Maturities [Abstract]
Amortized Cost, Due in one year or less	$ 16,862
Amortized Cost, Due after one year through five years	47,867
Amortized Cost, Due after five years through ten years	57,679
Amortized Cost, Due after ten years	124,166
Amortized Cost, Structured Securities	55,863
Amortized Cost, Subtotal	302,437
Estimated Fair Value, Due in one year or less	17,061
Estimated Fair Value, Due after one year through five years	48,490
Estimated Fair Value, Due after five years through ten years	60,624
Estimated Fair Value, Due after ten years	144,765
Estimated Fair Value, Structured Securities	55,745
Estimated Fair Value of Fixed Maturity Securities AFS	$ 326,685	$ 327,820