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Earnings (loss) per share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net loss	$ (0.3)	$ (15.1)
Amount allocated to common stockholders (as percent)	100.00%	100.00%
Basic EPS:
Net loss allocated to common stockholders	$ (0.3)	$ (15.1)
Net loss allocated to common stockholders (shares)	87.6	87.3
Net loss allocated to common stockholders, per share (in USD per share)	$ 0.00	$ (0.17)
Effect of Dilutive Securities:
Share-based compensation	$ 0.0	$ 0.0
Share-based compensation (shares)	0.0	0.0
Diluted EPS:
Net loss allocated to common stockholders with assumed conversion	$ (0.3)	$ (15.1)
Net loss allocated to common stockholders with assumed conversion (shares)	87.6	87.3
Net loss allocated to common stockholders with assumed conversion, per share (in USD per share)	$ 0.00	$ (0.17)
Securities excluded from calculation of diluted EPS (shares)	1.4	1.2

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Amount of increase (decrease) to net income used for calculating diluted earnings per share (EPS), resulting from the assumed exercise of dilutive convertible securities excluding adjustments related to ESOP convertible preferred stock, stock options, and restrictive stock units.

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Additional shares included in the calculation of diluted EPS as a result of the potentially dilutive effect of share based payment arrangements using the treasury stock method.

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