Stockholders' Equity Stock Repurchase Program (Details) - USD ($) $ in Millions	Jan. 31, 2016	Jan. 22, 2016	Mar. 21, 2014	Jan. 31, 2011
2011 Program [Member]
Share Repurchase [Line Items]
Stock Repurchase Program, Authorized Amount				$ 400.0
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 163.8
2014 Program [Member]
Share Repurchase [Line Items]
Stock Repurchase Program, Authorized Amount			$ 300.0
Stock Repurchase Program, Remaining Authorized Repurchase Amount	58.6
2016 Program [Member]
Share Repurchase [Line Items]
Stock Repurchase Program, Authorized Amount		$ 500.0
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 494.0