Common Stock Repurchase Program Additional Information (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	9 Months Ended
	Oct. 31, 2014	Oct. 31, 2014
Equity, Class of Treasury Stock [Line Items]
Common Stock shares remained available for repurchase under repurchase plans (in shares)	16.0	16.0
Common Stock
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value	$ 47.2	$ 151.1
Retained Earnings
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value	$ 56.1	$ 156.5
Common Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired (in shares)	1.9	5.8
Repurchased shares of its common stock on the open market, average repurchase price per share (in usd per share)	$ 54.11	$ 52.81