Cash and Cash Equivalents, Investments, and Funds Held for Customers - Classification on Balance Sheets (Details) - USD ($) $ in Millions	Oct. 31, 2020	Jul. 31, 2020	Oct. 31, 2019
Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 5,174	$ 6,442	$ 1,630
Available-for-sale debt securities, amortized cost	813	800
Total cash and cash equivalents, investments, and funds held for customers, amortized cost	6,271	7,497
Cash equivalents:	5,174	6,442
Available-for-sale debt securities, fair value	819	808
Total cash and cash equivalents, investments, and funds held for customers, fair value	6,277	7,505
Investments
Cash and Cash Equivalents Items [Line Items]
Available-for-sale debt securities, amortized cost	613	600
Available-for-sale debt securities, fair value	619	608
Funds held for customers
Cash and Cash Equivalents Items [Line Items]
Available-for-sale debt securities, amortized cost	484	455
Available-for-sale debt securities, fair value	$ 484	$ 455