Stockholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	Oct. 31, 2019	Jul. 31, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2018	Jan. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	$ 3,142.5	$ 3,193.1	$ 3,130.9	$ 3,022.4	$ 3,071.5	$ 3,248.2
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	(131.8)		(108.2)	(131.9)
Deferred hedging loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	(4.0)
Deferred hedging loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity			(24.5)	(28.7)
Net unrealized loss on benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	(87.2)		(72.1)	(57.1)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Stockholders' equity	$ (223.0)	$ (237.0)	$ (204.8)	$ (217.7)	$ (196.7)	$ (138.0)