Long-Term Incentive Compensation (Summary of Liability-Classified Performance Unit Activity) (Details) - Liability-Classified Performance Units - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Number of Units
Number of Shares/Units, Unvested shares/units at January 1 (in shares)	5,142,000	2,803,000	0
Number of Shares/Units, Granted (in shares)	6,172,000	2,757,000	3,200,000
Number of Shares/Units, Vested (in shares)	0	(43,000)	0
Number of Shares/Units, Forfeited (in shares)	(2,615,000)	(375,000)	(397,000)
Number of Shares/Units, Unvested shares/units at December 31 (in shares)	8,699,000	5,142,000	2,803,000
Weighted Average Fair Value
Weighted Average Fair Value, Unvested shares/units at January 1 (in dollars per share)	$ 2.42	$ 3.41	$ 0
Weighted Average Fair Value, Granted (in dollars per share)	1.41	4.34	3.70
Weighted Average Fair Value, Vested (in dollars per share)	0	2.42	0
Weighted Average Fair Value, Forfeited (in dollars per share)	3.05	3.12	4.55
Weighted Average Fair Value, Unvested shares/units at December 31 (in dollars per share)	$ 2.57	$ 2.42	$ 3.41
Workforce Reduction
Number of Units
Number of Shares/Units, Forfeited (in shares)	(518,450)	(375,086)	(295,160)