Common Stock Repurchase Program (Additional Information) (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	6 Months Ended
	Jul. 31, 2018 USD ($) $ / shares shares	Jul. 31, 2018 USD ($) $ / shares shares
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired (in shares) | shares	1.1	1.3
Repurchased shares of its common stock on the open market, average repurchase price per share (in usd per share) | $ / shares	$ 131.52	$ 128.92
Common Stock
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value | $	$ 77.3	$ 93.7
Retained Earnings
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value | $	$ 69.4	$ 74.0
Common Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Common stock shares remained available for repurchase under repurchase plans (in shares) | shares	18.4	18.4