Net (Loss) Income Per Share - Computation of Net Income Per Share Amounts (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended									12 Months Ended
	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	[1]	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2017		Jan. 31, 2016	Jan. 31, 2015
Numerator:
Net (loss) income	$ (173.4)	$ (142.8)	$ (98.2)		$ (167.7)	$ (37.2)	$ (43.8)	$ (268.6)	$ 19.1	$ (582.1)		$ (330.5)	$ 81.8
Denominator:
Denominator for basic net (loss) income per share—weighted average shares										222.7		226.0	227.1
Effect of dilutive securities										0.0	[2]	0.0	5.3
Denominator for dilutive net (loss) income per share										222.7		226.0	232.4
Basic net (loss) income per share (usd per share)	$ (0.78)	$ (0.64)	$ (0.44)		$ (0.75)	$ (0.17)	$ (0.19)	$ (1.18)	$ 0.08	$ (2.61)		$ (1.46)	$ 0.36
Diluted net (loss) income per share (usd per share)	$ (0.78)	$ (0.64)	$ (0.44)		$ (0.75)	$ (0.17)	$ (0.19)	$ (1.18)	$ 0.08	$ (2.61)		$ (1.46)	$ 0.35

[1] Certain first quarter fiscal 2017 balances have been revised to reflect the adoption of ASU 2016-09. As the adoption occurred in the second quarter of fiscal 2017, we are required to reflect any adjustments as of February 1, 2016, the beginning of the annual period that includes the interim period of adoption, and are required to revise our reported quarterly results for the first quarter. The revision resulted in a $5.3 million decrease of stock-based compensation expense from the previously reported expense. See Note 1, "Business and Summary of Significant Accounting Policies" for further discussion on the adoption.

[2] (1)The effect of dilutive securities of 4.6 million and 4.7 million shares for the fiscal year ended January 31, 2017 and 2016, 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 these fiscal years.