Revenue (Cumulative Effect of Adoption) (Details) - USD ($) $ in Millions	Apr. 30, 2019	Aug. 01, 2018	Jul. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Inventories, net	$ 359.5	$ 326.8	$ 334.1
Prepaid expense and other current assets	76.0	66.3	52.3
Other current liabilities	157.1	86.9	224.6
Deferred income taxes	19.0	5.3	4.2
Retained earnings	$ 1,276.0	1,127.4	1,122.1
Calculated under Revenue Guidance in Effect before Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Inventories, net			334.1
Prepaid expense and other current assets			52.3
Other current liabilities			86.6
Deferred income taxes			4.2
Retained earnings			$ 1,122.1
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Inventories, net		(7.3)
Prepaid expense and other current assets		14.0
Other current liabilities		0.3
Deferred income taxes		1.1
Retained earnings		$ 5.3