Common Stock Repurchase Program Additional Information (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	9 Months Ended
	Oct. 31, 2015 USD ($) $ / shares shares	Oct. 31, 2015 USD ($) $ / shares shares
Common Stock
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value | $	$ 72.2	$ 161.3
Retained Earnings
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value | $	$ 77.8	$ 196.4
Common Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired (in shares) | shares	3.2	6.9
Repurchased shares of its common stock on the open market, average repurchase price per share (in usd per share) | $ / shares	$ 46.33	$ 51.59
Common Stock shares remained available for repurchase under repurchase plans (in shares) | shares	7.9	7.9