Common Stock Repurchase Program Additional Information (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Apr. 30, 2014
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired (in shares)	2.0
Common Stock shares remained available for repurchase under repurchase plans (in shares)	19.8
Common Stock
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value	$ 49.4
Retained Earnings
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value	$ 53.1
Common Stock Repurchase Program
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)	$ 51.26