Fair Value Measurements (Details) $ in Millions	9 Months Ended
	May 02, 2020 USD ($) Store building	May 04, 2019 USD ($) Store	Aug. 03, 2019 USD ($)	Aug. 04, 2018 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Operating lease right-of-use asset	$ 637.6		$ 0.0
Fair Value, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets	28.8	$ 18.3	187.6	$ 55.7
Operating lease right-of-use asset	$ 63.5		74.8
Number Of Under-Performing Stores | Store	1,851	635
Number Of Buildings | building	1
Asset Impairment Charges	$ 158.8	$ 37.4
Operating Lease, Impairment Loss	11.3
Fair Value, Nonrecurring | Discontinued Operations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets	$ 10.0		28.7
Number Of Under-Performing Stores | Store	421
Asset Impairment Charges	$ 18.7
Term Loan
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	$ 271.3		$ 850.3