Stockholders' Equity Share Repurchase Table (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Equity [Abstract]
Cost of repurchases	$ 183.6	$ 220.4	$ 27.0
Purchase and retirement of Common Stock, Shares	2.8	2.8	0.3
Average cost per share	$ 65.24	$ 78.40	$ 89.91