Common Stock Repurchase Program Additional Information (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	9 Months Ended
	Oct. 31, 2017 USD ($) $ / shares shares	Oct. 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 | $	$ 35.6	$ 117.6
Retained Earnings
Equity, Class of Treasury Stock [Line Items]
Repurchased shares of its common stock on the open market, value | $	$ 81.7	$ 310.3
Common Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased and retired (in shares) | shares	1.0	4.4
Repurchased shares of its common stock on the open market, average repurchase price per share (in usd per share) | $ / shares	$ 112.97	$ 96.39
Common Stock shares remained available for repurchase under repurchase plans (in shares) | shares	22.1	22.1