Stockholders' Equity Share Repurchase Table (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Apr. 30, 2018	Apr. 30, 2017
Equity [Abstract]
Cost of repurchases	$ 40.5	$ 11.5
Purchase and retirement of Common Stock, Shares	0.4	0.1
Average cost per share	$ 99.48	$ 93.48