Net (Loss) Income Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended	9 Months Ended
	Oct. 31, 2015	Jul. 31, 2015	Oct. 31, 2014	Jul. 31, 2015	Oct. 31, 2015		Oct. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net (loss) income	$ (43.8)	$ (268.6)	$ 10.7	$ (249.5)	$ (293.3)		$ 70.3
Denominator:
Denominator for basic net (loss) income per share—weighted average shares (shares)	225,300,000		226,900,000		226,500,000		227,100,000
Effect of dilutive securities (shares)	0		4,600,000		0	[1]	4,800,000
Denominator for dilutive net (loss) income per share (shares)	225,300,000		231,500,000		226,500,000		231,900,000
Basic net (loss) income per share (in usd per share)	$ (0.19)	$ (1.18)	$ 0.05	$ (1.10)	$ (1.29)		$ 0.31
Diluted net (loss) income per share (in usd per share)	$ (0.19)		$ 0.05		$ (1.29)		$ 0.30
Potentially dilutive shares excluded from the computation of diluted net income per share (shares)	3,400,000				4,000,000
Exercise Price Higher than Average Market Value
Denominator:
Potentially dilutive shares excluded from the computation of diluted net income per share (shares)	600,000		0		100,000		0

[1] The effect of dilutive securities of 3.4 million and 4.0 million shares for the three and nine months ended October 31, 2015, respectively, have been excluded from the calculation of diluted net (loss) income per share as those shares would have been anti-dilutive due to the net (loss) incurred during those periods.