Net Income Per Share Attributable To Common Stockholders (Scheule of Net Income (Loss) Reconcilation) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement Operating Activities Segment [Line Items]
Net income (loss) attributable to common stockholders	$ (200)	$ 773	$ 978
Participating basic earnings	0	(3)	(5)
Net income (loss) attributable to common stockholders	$ (200)	$ 770	$ 973