Investments (Contractual Maturity Dates For Fixed-Maturity And Short-Term Investments) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Amortized cost
Due in one year or less	$ 462
Due after one year through five years	2,974
Due after five years through ten years	3,850
Due after ten years	2,513
Total	9,799	$ 9,324
Fair value
Due in one year or less	469
Due after one year through five years	3,135
Due after five years through ten years	3,941
Due after ten years	2,540
Total	$ 10,085	$ 9,650
% of fair value
Due in one year or less	4.60%
Due after one year through five years	31.10%
Due after five years through ten years	39.10%
Due after ten years	25.20%
Total	100.00%