Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended
	Jul. 31, 2013	Jul. 31, 2013
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired (in shares)	3.1	6.3
Common Stock shares remained available for repurchase under repurchase plans (in shares)	26.0	26.0
Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value	$ 64.7	$ 126.2
Retained Earnings [Member]
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value	$ 45.9	$ 113.6
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)	$ 36.38	$ 38.33