Deferred Compensation Additional Information (Details) (USD $) In Millions, unless otherwise specified	Apr. 30, 2014	Jan. 31, 2014
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Marketable securities	$ 778.3
Rabbi Trust Member
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation liability current	4.6	1.9
Deferred compensation liability		38.9
Deferred compensation liability non-current	37.4	37.0
Rabbi Trust Member | Marketable Securities, Current
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Trading securities, fair value	$ 42.0