Shares and Stockholders' Equity (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Shares and Stockholders' Equity [Abstract]
Deferred compensation plan mark to market adjustment	$ 8	$ (1)	$ 10	$ (1)