Net Income Per Share (Reconciliation of Earnings Attributable to Common Stockholders, Basic and Diluted) (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net income (loss) attributable to common stockholders	$ (20)	$ 231	$ (170)	$ 412
Participating share-based earnings	0	(1)	0	(2)
Basic and diluted net income (loss) attributable to common stockholders	$ (20)	$ 230	$ (170)	$ 410
Basic and diluted weighted average shares outstanding	165	167	165	168