Financial Instruments - Available for Sale Securities (Detail) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Investments, All Other Investments [Abstract]
Cost method investments	$ 112.3	$ 117.2
Other than temporary impairment losses, investments	15.5	1.3
Available-for-sale securities gross gains (losses)	(0.3)	1.5	$ 0.1
Proceeds from sale and maturity of marketable securities	$ 1,100.0	$ 2,300.0