Deferred Compensation Additional Information (Details) - USD ($) $ in Millions	Jul. 31, 2015	Jan. 31, 2015
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Marketable securities	$ 1,479.3
Rabbi Trust Member
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation liability	44.7	$ 40.3
Deferred compensation liability current	5.4	5.3
Deferred compensation liability non-current	$ 39.3	$ 35.0