Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions		3 Months Ended
		Apr. 30, 2017	Apr. 30, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net loss		$ (129.6)	$ (167.7)
Denominator:
Denominator for basic net loss per share—weighted average shares (shares)		219.9	224.4
Effect of dilutive securities (shares)	[1]	0.0	0.0
Denominator for dilutive net loss per share (shares)		219.9	224.4
Basic net loss per share (in usd per share)		$ (0.59)	$ (0.75)
Diluted net loss per share (in usd per share)		$ (0.59)	$ (0.75)
Potentially dilutive shares excluded from the computation of diluted net income per share (shares)		4.1	3.2
Exercise Price Higher than Average Market Value
Denominator:
Potentially dilutive shares excluded from the computation of diluted net income per share (shares)		0.3	0.9

[1] The effect of dilutive securities of 4.1 million and 3.2 million shares in the three months ended April 30, 2017 and 2016, respectively, have been excluded from the calculation of diluted net loss per share as those shares would have been anti-dilutive due to the net loss incurred during those periods.