Stockholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	Apr. 30, 2020	Jan. 31, 2020	Apr. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	$ 3,168.9	$ 3,322.9	$ 3,158.6
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	(158.5)	(130.4)	(132.2)
Deferred hedging gain (loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	10.7	5.4	(20.5)
Net unrealized loss on benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	(143.9)	(148.2)	(91.3)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	$ (291.7)	$ (273.2)	$ (244.0)