Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Apr. 30, 2018	Apr. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net loss	$ (82.4)	$ (129.6)
Denominator:
Denominator for basic net loss per share—weighted average shares (shares)	218.6	219.9
Effect of dilutive securities (shares)	0.0	0.0
Denominator for dilutive net loss per share (shares)	218.6	219.9
Basic net loss per share (in usd per share)	$ (0.38)	$ (0.59)
Diluted net loss per share (in usd per share)	$ (0.38)	$ (0.59)
Potentially dilutive shares excluded from the computation of diluted net income per share (shares)	3.0	4.1
Treasury Stock
Denominator:
Potentially dilutive shares excluded from the computation of diluted net income per share (shares)	0.2	0.3