Stock-Based Compensation (Summary of Liability-Classified Restricted Stock Unit Activity) (Details) - Liability-Classified RSUs - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Number of Units
Number of Shares/Units, Unvested shares/units at January 1 (in shares)	8,202,000	0
Number of Shares/Units, Granted (in shares)	8,659,000	12,216,000
Number of Shares/Units, Vested (in shares)	(2,624,000)	(232,000)
Number of Shares/Units, Forfeited (in shares)	(1,245,000)	(3,782,000)
Number of Shares/Units, Unvested shares/units at December 31 (in shares)	12,992,000	8,202,000
Weighted Average Fair Value
Weighted Average Fair Value, Unvested shares/units at January 1 (in dollars per share)	$ 3.41	$ 0
Weighted Average Fair Value, Granted (in dollars per share)	4.34	3.69
Weighted Average Fair Value, Vested (in dollars per share)	4.09	5.14
Weighted Average Fair Value, Forfeited (in dollars per share)	3.48	4.86
Weighted Average Fair Value, Unvested shares/units at December 31 (in dollars per share)	$ 2.42	$ 3.41
Workforce Reduction
Number of Units
Number of Shares/Units, Forfeited (in shares)	(400,056)	(2,766,610)