Net (Loss) Income Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended
	Jul. 31, 2015		Jul. 31, 2014	Jul. 31, 2015		Jul. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net (loss) income	$ (235.5)		$ 31.3	$ (216.4)		$ 59.6
Denominator:
Denominator for basic net (loss) income per share—weighted average shares (shares)	227,000,000		227,300,000	227,100,000		227,100,000
Effect of dilutive securities (shares)	0	[1]	5,100,000	0	[1]	5,300,000
Denominator for dilutive net (loss) income per share (shares)	227,000,000		232,400,000	227,100,000		232,400,000
Basic net (loss) income per share (in usd per share)	$ (1.04)		$ 0.14	$ (0.95)		$ 0.26
Diluted net (loss) income per share (in usd per share)	$ (1.04)		$ 0.13	$ (0.95)		$ 0.26
Potentially dilutive shares excluded from the computation of diluted net income per share (shares)	4,100,000			4,500,000
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 4.1 million and 4.5 million shares for the three and six months ended July 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.