Stockholders' Deficit (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Apr. 30, 2018	Feb. 01, 2019	May 01, 2018	Feb. 01, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	$ (210.9)	$ (338.3)	$ (241.6)	$ (128.6)	$ (256.0)
Common shares issued under stock plans	21.1	(21.9)	(28.0)	(12.9)	10.3
Stock-based compensation expense	75.2	74.0	64.2	56.9	54.4
Post-combination expense related to equity awards assumed	0.8
Cumulative effect of accounting changes						$ (0.7)	$ 1.4	$ 176.1
Purchase price accounting adjustment		10.3
Net loss	(24.2)	64.7	(23.7)	(39.4)	(82.4)
Other comprehensive loss	(6.6)	22.5	(6.6)	(17.1)	(10.0)
Stock Issued During Period, Value, Acquisitions				44.8
Repurchase and retirement of common shares	(100.0)	(22.2)	(102.6)	(146.7)	(21.0)
Ending balance	$ (245.3)	$ (210.9)	$ (338.3)	$ (241.6)	$ (128.6)
Common stock and additional paid-in capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance (shares)	219.4	219.1	218.5	219.1	218.3
Beginning balance	$ 2,071.5	$ 2,009.1	$ 2,012.5	$ 2,001.0	$ 1,952.7
Common shares issued under stock plans (shares)	0.8	0.4	1.4	0.2	1.0
Common shares issued under stock plans	$ 21.1	$ (21.9)	$ (28.0)	$ (12.9)	$ 10.3
Stock-based compensation expense	75.2	74.0	$ 64.2	$ 56.9	$ 54.4
Post-combination expense related to equity awards assumed	$ 0.8
Purchase price accounting adjustment		$ 10.3
Stock Issued During Period, Shares, Acquisitions (shares)				0.3
Stock Issued During Period, Value, Acquisitions				$ 44.8
Repurchase and retirement of common shares (shares)	(0.6)	(0.1)	(0.8)	(1.1)	(0.2)
Repurchase and retirement of common shares	$ (45.5)	$ 0.0	$ (39.6)	$ (77.3)	$ (16.4)
Ending balance (shares)	219.6	219.4	219.1	218.5	219.1
Ending balance	$ 2,123.1	$ 2,071.5	$ 2,009.1	$ 2,012.5	$ 2,001.0
Accumulated other comprehensive loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(135.0)	(157.5)	(150.9)	(133.8)	(123.8)
Other comprehensive loss	(6.6)	22.5	(6.6)	(17.1)	(10.0)
Ending balance	(141.6)	(135.0)	(157.5)	(150.9)	(133.8)
Accumulated deficit
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning balance	(2,147.4)	(2,189.9)	(2,103.2)	(1,995.8)	(2,084.9)
Cumulative effect of accounting changes						$ (0.7)		$ 176.1
Net loss	(24.2)	64.7	(23.7)	(39.4)	(82.4)
Repurchase and retirement of common shares	(54.5)	(22.2)	(63.0)	(69.4)	(4.6)
Ending balance	$ (2,226.8)	$ (2,147.4)	$ (2,189.9)	$ (2,103.2)	$ (1,995.8)