Deferred Compensation Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Jul. 31, 2013	Jan. 31, 2013
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Marketable Securities	$ 1,007.0
Rabbi Trust Member
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation liability current	4.4	3.9
Deferred compensation liability		35.3
Deferred compensation liability non-current	35.5	31.4
Rabbi Trust Member | Marketable Securities, Current [Member]
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Trading Securities, Fair Value Disclosure	$ 39.9