Net Income Per Share Attributable To Common Stockholders (Scheule of Net Income (Loss) Reconcilation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Operating Activities Segment [Line Items]
Net income (loss) attributable to common stockholders	$ 978	$ 833	$ (556)
Participating basic earnings	(5)	(6)	0
Net income (loss) attributable to common stockholders	$ 973	$ 827	$ (556)