Cash and Cash Equivalents, Investments, and Funds Held for Customers - Classification on Balance Sheets (Details) - USD ($) $ in Millions	Apr. 30, 2020	Jul. 31, 2019	Apr. 30, 2019
Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 3,371	$ 2,116	$ 2,946
Available-for-sale debt securities, amortized cost	796	822
Total cash and cash equivalents, investments, and funds held for customers, amortized cost	4,375	3,187
Cash and cash equivalents, fair value	3,371	2,116
Available-for-sale debt securities, fair value	800	824
Total cash and cash equivalents, investments, and funds held for customers, fair value	4,379	3,189
Investments
Cash and Cash Equivalents Items [Line Items]
Available-for-sale debt securities, amortized cost	597	622
Available-for-sale debt securities, fair value	600	624
Funds held for customers
Cash and Cash Equivalents Items [Line Items]
Available-for-sale debt securities, amortized cost	388	436
Available-for-sale debt securities, fair value	389	436
Long-term investments
Cash and Cash Equivalents Items [Line Items]
Available-for-sale debt securities, amortized cost	19	13
Available-for-sale debt securities, fair value	$ 19	$ 13