CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Millions, $ in Millions	Total	Common stock and additional paid-in capital	Accumulated other comprehensive loss	Retained earnings (Accumulated deficit)
Balance (in shares) at Jan. 31, 2014		226.7
Beginning Balance at Jan. 31, 2014	$ 2,261.5	$ 1,637.3	$ (0.6)	$ 624.8
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares issued under stock plans (in shares)		7.2
Common shares issued under stock plans	135.4	$ 135.4
Stock-based compensation expense	165.6	$ 165.6
Net (loss) income	81.8			81.8
Other comprehensive (loss)	(52.7)		(52.7)
Repurchase and retirement of common shares (in shares)		(6.9)
Repurchase and retirement of common shares	(372.4)	$ (165.2)		(207.2)
Balance (in shares) at Jan. 31, 2015		227.0
Ending Balance at Jan. 31, 2015	2,219.2	$ 1,773.1	(53.3)	499.4
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares issued under stock plans (in shares)		5.9
Common shares issued under stock plans	59.2	$ 59.2
Stock-based compensation expense	197.2	$ 197.2
Net (loss) income	(330.5)			(330.5)
Other comprehensive (loss)	(67.8)		(67.8)
Repurchase and retirement of common shares (in shares)		(8.5)
Repurchase and retirement of common shares	(458.0)	$ (208.3)		(249.7)
Tax benefits from employee stock plans	$ 0.3	$ 0.3
Balance (in shares) at Jan. 31, 2016	224.4	224.4
Ending Balance at Jan. 31, 2016	$ 1,619.6	$ 1,821.5	(121.1)	(80.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares issued under stock plans (in shares)		5.6
Common shares issued under stock plans	43.4	$ 43.4
Stock-based compensation expense	221.8	$ 221.8
Net (loss) income	(582.1)			(582.1)
Other comprehensive (loss)	(57.4)		(57.4)
Repurchase and retirement of common shares (in shares)		(9.7)
Repurchase and retirement of common shares	(631.6)	$ (217.3)		(414.3)
Cumulative effect of accounting changes	$ 119.9	$ 6.9		113.0
Balance (in shares) at Jan. 31, 2017	220.3	220.3
Ending Balance at Jan. 31, 2017	$ 733.6	$ 1,876.3	$ (178.5)	$ (964.2)