Stockholders' Equity Stock Repurchase Program (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2018	Jan. 22, 2016	Mar. 21, 2014
2014 Program [Member]
Share Repurchase [Line Items]
Stock Repurchase Program, Authorized Amount			$ 300.0
2016 Program [Member]
Share Repurchase [Line Items]
Stock Repurchase Program, Authorized Amount		$ 500.0
Stock Repurchase Program Expiration Date	Jan. 31, 2019
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 211.2