Investments (Maturities of Fixed Maturity Securities) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Amortized cost, due in one year or less	$ 1,896
Amortized cost, due after one year through five years	7,024
Amortized cost, due after five years through ten years	12,782
Amortized cost, due after ten years	26,463
Amortized cost, Structured Securities	16,017
Fixed maturity securities, amortized cost	64,182	$ 63,083
Estimated fair value, due in one year or less	1,886
Estimated fair value, due after one year through five years	6,981
Estimated fair value, due after five years through ten years	12,923
Estimated fair value, due after ten years	31,899
Estimated fair value, Structured Securities	16,513
Fixed maturity securities, estimated fair value	$ 70,202	$ 69,977