Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Apr. 30, 2013
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired (in shares)	3.2
Common Stock shares remained available for repurchase under repurchase plans (in shares)	29.0
Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value	61.5
Retained Earnings [Member]
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value	67.7
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)	40.18