Earnings Per Share - Summary of Computations of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Numerator:
Net income (loss) from continuing operations	$ 1.8	$ 17.0	$ 57.7	$ (53.0)
Net (loss) income from discontinued operations	0.0	(0.7)	0.0	5.4
Net income (loss)	$ 1.8	$ 16.3	$ 57.7	$ (47.6)
Denominator:
Weighted average common shares outstanding - basic (in shares)	168.9	169.8	168.8	159.5
Effect of dilutive securities: stock compensation plans (in shares)	0.7	0.9	0.8	0.0
Weighted average common shares outstanding - diluted (in shares)	169.6	170.7	169.6	159.5
Basic:
Basic income (loss) per common share from continuing operations (in dollars per share)	$ 0.01	$ 0.10	$ 0.34	$ (0.33)
Basic income per common share from discontinued operations (in dollars per share)	0	0	0	0.03
Basic income (loss) per common share (in dollars per share)	0.01	0.10	0.34	(0.30)
Diluted:
Diluted income (loss) per common share from continuing operations (in dollars per share)	0.01	0.10	0.34	(0.33)
Diluted income per common share from discontinued operations (in dollars per share)	0	0	0	0.03
Diluted income (loss) per common share (in dollars per share)	$ 0.01	$ 0.10	$ 0.34	$ (0.30)