Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Apr. 30, 2012
Stockholders Equity Note [Line Items]
Common stock repurchased and retired (in shares)	2.5
Common Stock Repurchase Program
Stockholders Equity Note [Line Items]
Repurchased shares of its common stock on the open market, average repurchase price per share (in usd per share)	39.79
Common Stock shares remained available for repurchase under repurchase plans (in shares)	12.2
Common Stock [Member]
Stockholders Equity Note [Line Items]
Repurchased shares of its common stock on the open market, value	(54.1)
Retained Earnings
Stockholders Equity Note [Line Items]
Repurchased shares of its common stock on the open market, value	(45.1)