Description of Business and Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jan. 31, 2020	Jan. 31, 2019	Jan. 31, 2020	Jan. 31, 2019	Aug. 01, 2019	Jul. 31, 2019
Capitalized Contract Cost [Line Items]
Net change in customer fund deposits			$ 25	$ 67
Deferred revenue recognized	$ 154	$ 149	$ 509	476
Timing of performance obligation			12 months
Long-term deferred revenue	4		$ 4			$ 4
Notes receivable	103		103			95
Operating lease right-of-use assets	297		297
Present value of lease liabilities	343		343
Deferred rent liability	$ 0		$ 0			$ (47)
Accounting Standards Update 2016-02
Capitalized Contract Cost [Line Items]
Operating lease right-of-use assets					$ 319
Present value of lease liabilities					361
Deferred rent liability					47
Prepaid rent					$ 5
Restatement adjustment
Capitalized Contract Cost [Line Items]
Net change in customer fund deposits				$ 67
Largest Customer | Customer Concentration Risk | Accounts Receivable
Capitalized Contract Cost [Line Items]
Concentration risk, percentage			11.00%