Deferred Compensation - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Jan. 31, 2012	Jan. 31, 2011
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Marketable Securities	$ 447.2
Rabbi Trust
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred Compensation Liability, Current and Noncurrent		31.3
Deferred compensation liability current	3.2	3.4
Deferred compensation liability non-current	28.3	27.9
Marketable Securities, Current
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Trading Securities, Fair Value Disclosure		31.3
Marketable Securities, Current | Rabbi Trust
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Trading Securities, Fair Value Disclosure	$ 31.5