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		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Numerator:
Net income (loss) from continuing operations	$ 28.9	$ 2.5	$ 86.6	$ (50.5)
Net income from discontinued operations	0.0	0.0	0.0	5.4
Net income (loss)	$ 28.9	$ 2.5	$ 86.6	$ (45.1)
Denominator:
Weighted average common shares outstanding - basic (in shares)	169.0	168.6	168.9	162.6
Effect of dilutive securities: stock compensation plans (in shares)	0.8	0.9	0.8	0.0
Weighted average common shares outstanding - diluted (in shares)	169.8	169.5	169.7	162.6
Basic:
Basic income (loss) per common share from continuing operations (in dollars per share)	$ 0.17	$ 0.01	$ 0.51	$ (0.31)
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)	0.17	0.01	0.51	(0.28)
Diluted:
Diluted income (loss) per common share from continuing operations (in dollars per share)	0.17	0.01	0.51	(0.31)
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)	$ 0.17	$ 0.01	$ 0.51	$ (0.28)