Acquisitions and Divestitures - (Schedule of Pro Forma) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Business Combinations [Abstract]
Revenues	$ 2,701	$ 3,673
Net income (loss) attributable to common stock	$ (3,177)	$ 995
Net income (loss) attributable to common stock per share – basic (in dollars per share)	$ (4.71)	$ 1.48
Net income (loss) attributable to common stock per share – diluted (in dollars per share)	$ (4.71)	$ 1.48