Stockholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions		Jul. 31, 2018	Jan. 31, 2018	Jul. 31, 2017
Equity [Abstract]
Foreign currency translation adjustments		$ (106.3)	$ (48.0)	$ (92.4)
Unrealized (loss) gain on marketable securities a	[1]	0.0	(1.8)	0.5
Deferred hedging loss		(30.6)	(22.9)	(18.1)
Net unrealized loss on benefit plans		(59.8)	(65.3)	(93.2)
Accumulated other comprehensive (loss) gain, net of tax		$ (196.7)	$ (138.0)	$ (203.2)

[1] The Company adopted ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities, on February 1, 2018 using the modified retrospective method. Under ASU 2016-01, the Company recognizes both realized and unrealized gains and losses on marketable securities in Other (income) expense, net. Previously, unrealized gains and losses were recorded as a separate component of stockholders' equity