Organization and Summary of Significant Accounting Policies (Summary of Cash and Cash Equivalents) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Organization and Summary of Significant Accounting Policies [Abstract]
Cash	$ 261	$ 254
Marketable securities	605	1,169
Other cash equivalents	50
Total	$ 916	$ 1,423	$ 15	$ 53