Stockholders' Equity Share Repurchase Table (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Equity [Abstract]
Cost of repurchases	$ 99.2	$ 183.6	$ 220.4
Purchase and retirement of Common Stock, Shares	1.0	2.8	2.8
Average cost per share	$ 94.86	$ 65.24	$ 78.40