Cash And Cash Equivalents (Summary Of Cash And Cash Equivalents) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Cash And Cash Equivalents [Abstract]
Cash	$ 31	$ 15
Marketable securities	1,443
Total cash and cash equivalents	$ 1,474	$ 15	$ 15	$ 53