Stock-based Compensation Expense Intrinsic Value of Options Exercised and Weighted Average Grant Date Fair Value of Stock Options Granted (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jul. 31, 2015	Jul. 31, 2014	Jul. 31, 2015	Jul. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Pre-tax intrinsic value of options exercised	[1]	$ 3.6	$ 21.4	$ 17.4	$ 44.2

[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.