Stock-based Compensation Expense Intrinsic Value of Options Exercised and Weighted Average Grant Date Fair Value of Stock Options Granted (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Apr. 30, 2013		Apr. 30, 2012
Stock Based Compensation Expense [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value (in usd)	$ 32.8	[1]	$ 60.3	[1]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in usd per share)			$ 13.43	[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.

[2] The weighted average grant date fair value of stock options granted is calculated, as of the stock option grant date, using the Black-Scholes-Merton option pricing model.