Investments (Contractual Maturity Dates For Fixed-Maturity And Short-Term Investments) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Amortized cost
Due in one year or less	$ 581
Due after one year through five years	3,450
Due after five years through ten years	3,789
Due after ten years	3,492
Total	11,312	$ 11,108
Fair value
Due in one year or less	589
Due after one year through five years	3,697
Due after five years through ten years	4,178
Due after ten years	3,874
Total	$ 12,338	$ 11,698
% of fair value
Due in one year or less	4.80%
Due after one year through five years	30.00%
Due after five years through ten years	33.90%
Due after ten years	31.30%
Total	100.00%