Common Stock Repurchase Program Additional Information (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	6 Months Ended
	Jul. 31, 2014	Jul. 31, 2014
Equity, Class of Treasury Stock [Line Items]
Common Stock shares remained available for repurchase under repurchase plans (in shares)	17.9	17.9
Common Stock
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value	$ 54.5	$ 103.9
Retained Earnings
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value	$ 47.3	$ 100.4
Common Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired (in shares)	1.9	3.9
Repurchased shares of its common stock on the open market, average repurchase price per share (in usd per share)	$ 53.15	$ 52.18