CONSOLIDATED STATEMENTS OF STOCKHOLDERS' (DEFICIT) EQUITY - USD ($) $ in Millions	Total	Common stock and additional paid-in capital	Accumulated other comprehensive loss	Accumulated deficit
Beginning Balance (in shares) at Jan. 31, 2017		220,300,000
Beginning 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)		4,900,000
Common shares issued under stock plans	(48.7)	$ (48.7)
Stock-based compensation expense	261.4	$ 261.4
Net income (loss)	(566.9)			(566.9)
Other comprehensive income (loss)	54.7		54.7
Repurchase and retirement of common shares (in shares)		(6,900,000)
Repurchase and retirement of common shares	(690.1)	$ (136.3)		(553.8)
Ending Balance (in shares) at Jan. 31, 2018		218,300,000
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)		3,000,000.0
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 adoption of accounting standards	177.5			177.5
Net income (loss)	(80.8)			(80.8)
Other comprehensive income (loss)	(11.2)		(11.2)
Shares issued as consideration for business combination (in shares)		300,000
Shares issued as consideration for business combination	44.8	$ 44.8
Repurchase and retirement of common shares (in shares)		(2,200,000)
Repurchase and retirement of common shares	$ (292.5)	$ (133.3)		(159.2)
Ending Balance (in shares) at Jan. 31, 2019	219,400,000.0	219,400,000
Ending Balance at Jan. 31, 2019	$ (210.9)	$ 2,071.5	(135.0)	(2,147.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common shares issued under stock plans (in shares)		2,700,000
Common shares issued under stock plans	(18.6)	$ (18.6)
Stock-based compensation expense	332.7	332.7
Settlement of liability-classified restricted stock units	23.5	23.5
Pre-combination expense related to equity awards assumed	1.2	$ 1.2
Cumulative effect of adoption of accounting standards	(0.7)			(0.7)
Net income (loss)	214.5			214.5
Other comprehensive income (loss)	(25.3)		(25.3)
Repurchase and retirement of common shares (in shares)		(2,700,000)
Repurchase and retirement of common shares	$ (455.5)	$ (93.3)		(362.2)
Ending Balance (in shares) at Jan. 31, 2020	219,400,000.0	219,400,000
Ending Balance at Jan. 31, 2020	$ (139.1)	$ 2,317.0	$ (160.3)	$ (2,295.8)