CONSOLIDATED STATEMENTS OF STOCKHOLDERS' (DEFICIT) EQUITY - USD ($) shares in Millions, $ in Millions	Total	Common stock and additional paid-in capital	Accumulated other comprehensive loss	Accumulated deficit
Beginning Balance (in shares) at Jan. 31, 2016		224.4
Beginning 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
Tax benefits from employee stock plans	119.9	$ 6.9		113.0
Net loss	(582.1)			(582.1)
Other comprehensive income (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)
Ending Balance (in shares) at Jan. 31, 2017		220.3
Ending Balance at Jan. 31, 2017	733.6	$ 1,876.3	(178.5)	(964.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares issued under stock plans (in shares)		4.9
Common shares issued under stock plans	(48.7)	$ (48.7)
Stock-based compensation expense	261.4	$ 261.4
Net loss	(566.9)			(566.9)
Other comprehensive income (loss)	54.7		54.7
Repurchase and retirement of common shares (in shares)		(6.9)
Repurchase and retirement of common shares	$ (690.1)	$ (136.3)		(553.8)
Ending Balance (in shares) at Jan. 31, 2018	218.3	218.3
Ending Balance at Jan. 31, 2018	$ (256.0)	$ 1,952.7	(123.8)	(2,084.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares issued under stock plans (in shares)		3.0
Common shares issued under stock plans	(52.5)	$ (52.5)
Stock-based compensation expense	249.5	249.5
Pre-combination expense related to equity awards assumed	10.3	$ 10.3
Cumulative effect of accounting changes	177.5			177.5
Net loss	(80.8)			(80.8)
Other comprehensive income (loss)	(11.2)		(11.2)
Shares issued as consideration for business combination (in shares)		0.3
Shares issued as consideration for business combination	44.8	$ 44.8
Repurchase and retirement of common shares (in shares)		(2.2)
Repurchase and retirement of common shares	$ (292.5)	$ (133.3)		(159.2)
Ending Balance (in shares) at Jan. 31, 2019	219.4	219.4
Ending Balance at Jan. 31, 2019	$ (210.9)	$ 2,071.5	$ (135.0)	$ (2,147.4)