Debt - Interest Rates of the Credit Agreement (Details)	6 Months Ended	12 Months Ended
	Jan. 27, 2018	Jul. 29, 2017	Jul. 30, 2016
Credit Agreement - Revolving facility (matures April 2020)
Line of Credit Facility [Line Items]
Unutilized commitment fee (in percent)	0.35%	0.35%	0.40%
Minimum | Standby Letters of Credit
Line of Credit Facility [Line Items]
Unutilized commitment fee (in percent)	1.25%
Minimum | Commercial Letters of Credit
Line of Credit Facility [Line Items]
Unutilized commitment fee (in percent)	0.625%
Minimum | Credit Agreement - Revolving facility (matures April 2020)
Line of Credit Facility [Line Items]
Unutilized commitment fee (in percent)	0.25%
Maximum | Standby Letters of Credit
Line of Credit Facility [Line Items]
Unutilized commitment fee (in percent)	2.00%
Maximum | Commercial Letters of Credit
Line of Credit Facility [Line Items]
Unutilized commitment fee (in percent)	1.00%
Maximum | Credit Agreement - Revolving facility (matures April 2020)
Line of Credit Facility [Line Items]
Unutilized commitment fee (in percent)	0.40%
Eurodollar
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Eurodollar | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.25%
Eurodollar | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.00%
Administrative Agent Base Rate | Minimum
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.25%
Administrative Agent Base Rate | Maximum
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Federal Funds
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%