Share-Based Compensation - Stock Option Activity Table (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning balance	16,285
Granted (in shares options)	3,611
Exercised (in shares options)	0
Expired (in shares options)	(64)
Forfeited (in shares options)	(267)
Outstanding, ending balance	19,565	16,285
Exercisable (in shares options)	8,776
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Weighted average exercise price, beginning (in dollars per share)	$ 8.25
Weighted average exercise price, granted (in dollars per share)	3.01
Weighted average exercise price, exercised (in dollars per share)	0.00
Weighted average exercise price, expired (in dollars per share)	20.77
Weighted average exercise price, forfeited (in dollars per share)	5.45
Weighted average exercise price, ending (in dollars per share)	7.28	$ 8.25
Weighted average exercise price, exercisable (in dollars per share)	$ 10.88
Weighted average contract life, outstanding (in years)	7 years 11 months 4 days	7 years 8 months 23 days
Weighted average contract life, exercisable (in years)	6 years 6 months 7 days
Aggregate intrinsic value, outstanding, beginning balance	$ 1
Aggregate intrinsic value, exercised	0
Aggregate intrinsic value, outstanding, ending balance	0	$ 1
Aggregate intrinsic value, exercisable	$ 0