Stockholders' Equity - Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions		Apr. 30, 2018	Jan. 31, 2018	Apr. 30, 2017
Accumulated other comprehensive (loss) earnings, net of tax:
Foreign currency translation adjustments		$ (73.0)	$ (48.0)	$ (131.6)
Unrealized (loss) gain on marketable securities a	[1]	0.0	(1.8)	0.9
Deferred hedging loss		(30.2)	(22.9)	(17.1)
Net unrealized loss on benefit plans		(62.9)	(65.3)	(95.0)
Accumulated other comprehensive (loss) gain, net of tax		$ (166.1)	$ (138.0)	$ (242.8)

[1] a 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 expense, net. Previously, unrealized gains and losses were recorded as a separate component of stockholders' equity.