Investments (Contractual Maturity Dates For Fixed-Maturity And Short-Term Investments) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Amortized cost
Due in one year or less	$ 586
Due after one year through five years	2,894
Due after five years through ten years	3,663
Due after ten years	3,500
Total	10,643	$ 10,314
Fair value
Due in one year or less	592
Due after one year through five years	2,912
Due after five years through ten years	3,653
Due after ten years	3,532
Total	$ 10,689	$ 10,699
% of fair value
Due in one year or less	5.50%
Due after one year through five years	27.30%
Due after five years through ten years	34.20%
Due after ten years	33.00%
Total	100.00%