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		6 Months Ended
	Jul. 31, 2012	Jul. 31, 2011	Jul. 31, 2012		Jul. 31, 2011
Stock Based Compensation Expense [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	$ 5.6	$ 13.0	$ 65.9	[1]	$ 72.5
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value (in usd per share)	$ 10.86	$ 11.95	$ 13.40	[2]	$ 14.26

[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.