Loss (Earnings) Per Share - Computation of Weighted Average Shares Outstanding (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Schedule of Earnings Per Share [Line Items]
Net (loss) income attributable to common stockholders	$ (69.2)	$ 104.7	$ (154.7)	$ (39.0)
Numerator adjustments for diluted EPS:
Gain on settlement agreement related to Series B Convertible Preferred Stock	0.0	(103.0)	0.0	(103.0)
Gain on amendment of Series B Convertible Preferred Stock	0.0	(32.9)	0.0	(32.9)
Remeasurement adjustment associated with the Preferred Series B redemption liability	0.0	(6.0)	0.0	(6.0)
Income allocated to PDH non-controlling interest	0.0	(1.5)	0.0	0.0
Net loss attributable to common stockholders for diluted EPS	$ (69.2)	$ (38.7)	$ (154.7)	$ (180.9)
Basic weighted average common stock outstanding (in shares)	286.7	234.4	285.8	231.2
Denominator adjustments for diluted EPS:
Issuable upon conversion of the PDH non-controlling interest (in shares)	0.0	8.0	0.0	0.0
Share adjustments (in shares)	0.0	30.1	0.0	22.1
Dilutive weighted average common shares outstanding (in shares)	286.7	264.5	285.8	253.3
(Loss) earnings per share attributable to common stockholders:
Basic (in dollars per share)	$ (0.24)	$ 0.45	$ (0.54)	$ (0.17)
Diluted (in dollars per share)	(0.24)	(0.15)	(0.54)	(0.71)
Dividends per share paid to common stockholders	$ 0	$ 0	$ 0	$ 0
Series B Preferred Stock
Denominator adjustments for diluted EPS:
Assumed conversion related to the amendment of Series B preferred shares (in shares)	0.0	17.1	0.0	20.4
Assumed settlement of preferred stock redemption liability (in shares)	0.0	5.0	0.0	1.7