Cash And Cash Equivalents (Summary Of Cash And Cash Equivalents) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Cash And Cash Equivalents [Abstract]
Cash	$ 57	$ 15
Marketable securities	1,540
Total cash and cash equivalents	$ 1,597	$ 15	$ 17	$ 53