Cash And Cash Equivalents (Summary Of Cash And Cash Equivalents) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Cash And Cash Equivalents [Abstract]
Cash	$ 263	$ 254
Marketable securities	798	1,169
Other cash equivalents	50
Total cash and cash equivalents	$ 1,111	$ 1,423	$ 998	$ 15