Stock-based Compensation Expense Intrinsic Value of Options Exercised and Weighted Average Grant Date Fair Value of Stock Options Granted (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2013		Jul. 31, 2012
Stock Based Compensation Expense [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value (in usd)	$ 10.0	$ 5.6	$ 42.8	[1]	$ 65.9	[1]

[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.