Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Apr. 30, 2020	Apr. 30, 2019
Numerator:
Net income (loss)	$ 66.5	$ (24.2)
Denominator:
Denominator for basic net loss per share—weighted average shares (shares)	219,200,000	219,600,000
Effect of dilutive securities (shares)	2,100,000	0
Denominator for dilutive net loss per share (shares)	221,300,000	219,600,000
Basic net income (loss) per share (in usd per share)	$ 0.30	$ (0.11)
Diluted net income (loss) per share (in usd per share)	$ 0.30	$ (0.11)
Dilutive securities excluded from earnings per share sue to net loss scenario (in shares)		2,300,000
Potentially dilutive shares excluded from the computation of diluted net income per share (shares)	0	0