Investments (Contractual Maturity Dates For Fixed-Maturity And Short-Term Investments) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Amortized cost
Due in one year or less	$ 455
Due after one year through five years	3,180
Due after five years through ten years	3,792
Due after ten years	3,681
Total	11,108	$ 10,643
Fair value
Due in one year or less	459
Due after one year through five years	3,302
Due after five years through ten years	4,011
Due after ten years	3,926
Total	$ 11,698	$ 10,689
% of fair value
Due in one year or less	3.90%
Due after one year through five years	28.20%
Due after five years through ten years	34.30%
Due after ten years	33.60%
Total	100.00%