Deferred Compensation - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Jan. 31, 2014	Jan. 31, 2013
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Marketable securities	$ 691.4
Rabbi Trust
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation liability current	1.9	3.9
Deferred compensation liability non-current	37.0	31.4
Marketable Securities, Current
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Trading securities	35.6	31.1
Marketable Securities, Current | Rabbi Trust
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Trading securities	$ 38.9	$ 35.3