Stockholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	$ 3,193.1	$ 3,172.0	$ 3,130.9	$ 3,071.5	$ 3,268.6	$ 3,248.2
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	(134.9)		(108.2)	(106.3)
Deferred hedging loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	(12.9)
Deferred hedging loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity			(24.5)	(30.6)
Net gain (loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	(89.2)		(72.1)	(59.8)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	$ (237.0)	$ (244.0)	$ (204.8)	$ (196.7)	$ (166.1)	$ (138.0)