Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended	9 Months Ended
	Oct. 31, 2016	Apr. 30, 2016	Oct. 31, 2015	Jul. 31, 2015	Jul. 31, 2015	Oct. 31, 2016		Oct. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net loss	$ (142.8)	$ (167.7)	$ (43.8)	$ (268.6)	$ (249.5)	$ (408.7)		$ (293.3)
Denominator:
Denominator for basic net loss per share—weighted average shares (shares)	222.3		225.3			223.3		226.5
Effect of dilutive securities (shares)	0.0		0.0			0.0	[1]	0.0	[1]
Denominator for dilutive net loss per share (shares)	222.3		225.3			223.3		226.5
Basic net loss per share (in usd per share)	$ (0.64)		$ (0.19)			$ (1.83)		$ (1.29)
Diluted net loss per share (in usd per share)	$ (0.64)		$ (0.19)			$ (1.83)		$ (1.29)
Potentially dilutive shares excluded from the computation of diluted net income per share (shares)	4.4		3.4					4.0
Exercise Price Higher than Average Market Value
Denominator:
Potentially dilutive shares excluded from the computation of diluted net income per share (shares)	0.0		0.6			0.4		0.1

[1] The effect of dilutive securities of 4.4 million shares and 3.4 million shares for the three months ended October 31, 2016 and 2015, 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. The effect of dilutive securities of 4.0 million shares in each of the nine months ended October 31, 2016 and 2015 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.