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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, 2015
Apr. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]    
Pre-tax intrinsic value of options exercised $ 13.8us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue [1] $ 22.8us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue [1]
Weighted average grant date fair value per share of stock options granted (in dollars per share) $ 0.0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue [2] $ 0.0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue [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 per share of stock options granted is calculated, as of the stock option grant date, using the Black-Scholes Merton ("BSM") option pricing model. For the three months ended April 30, 2015 and 2014, Autodesk did not grant stock options.