Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended
	Oct. 31, 2013	Oct. 31, 2013
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired (in shares)	2.0	8.3
Common Stock shares remained available for repurchase under repurchase plans (in shares)	24.0	24.0
Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value	$ 49.4	$ 175.6
Retained Earnings [Member]
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value	$ 29.5	$ 143.1
Common Stock Repurchase Program [member]
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, average repurchase price per share (in usd per share)	$ 39.37	$ 38.58