Deferred Compensation Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Jul. 31, 2012	Jan. 31, 2012
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Marketable Securities	$ 786.6
Rabbi Trust Member
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation liability current	3.3	3.2
Deferred compensation liability		31.5
Deferred compensation liability non-current	31.4	28.3
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	$ 34.7