Stockholders' Equity Share Repurchase Table (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Equity [Abstract]
Cost of repurchases	$ 21.0	$ 71.8	$ 32.5	$ 149.9
Purchase and retirement of Common Stock, Shares	0.2	1.1	0.4	2.3
Average cost per share	$ 91.27	$ 62.71	$ 92.04	$ 64.62