Common Stock Repurchase Program Additional Information (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	6 Months Ended
	Jul. 31, 2017 USD ($) $ / shares shares	Jul. 31, 2017 USD ($) $ / shares shares
Common Stock
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value | $	$ 20.8	$ 82.0
Retained Earnings
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value | $	$ 97.8	$ 228.6
Common Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired (in shares) | shares	1.2	3.4
Repurchased shares of its common stock on the open market, average repurchase price per share (in usd per share) | $ / shares	$ 102.71	$ 91.33
Common Stock shares remained available for repurchase under repurchase plans (in shares) | shares	23.2	23.2