Common Stock Repurchase Program Additional Information (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	6 Months Ended
	Jul. 31, 2016 USD ($) $ / shares shares	Jul. 31, 2016 USD ($) $ / shares shares
Common Stock
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value | $	$ 65.8	$ 111.5
Retained Earnings
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value | $	$ 104.1	$ 158.5
Common Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired (in shares) | shares	3.0	4.8
Repurchased shares of its common stock on the open market, average repurchase price per share (in usd per share) | $ / shares	$ 55.88	$ 56.20
Common Stock shares remained available for repurchase under repurchase plans (in shares) | shares	1.5	1.5