Employee and Director Stock Plans - Intrinsic Value of Options Exercised and Weighted Average Grant Date Fair Value of Stock Options Granted (Detail) - USD ($) $ in Millions		12 Months Ended
		Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Intrinsic value of options exercised	[1]	$ 32.6	$ 67.6	$ 149.0

[1] The intrinsic value of options exercised is calculated as the difference between the exercise price of the option and the market value of the stock on the date of exercise.