Cash and Cash Equivalents, Investments, and Funds Held for Customers - Classification on Balance Sheets (Details) - USD ($) $ in Millions	Apr. 30, 2019	Jul. 31, 2018	Apr. 30, 2018
Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents	$ 2,946	$ 1,464	$ 1,614
Cash and cash equivalents, fair value	2,946	1,464
Available-for-sale debt securities, amortized cost	600	454
Available-for-sale debt securities	600	452
Total cash and cash equivalents, investments, and funds held for customers, Amortized Cost	3,742	2,098
Total cash and cash equivalents, investments, and funds held for customers, Fair Value	3,742	2,096
Investments
Cash and Cash Equivalents Items [Line Items]
Available-for-sale debt securities, amortized cost	400	253
Available-for-sale debt securities	400	252
Funds held for customers
Cash and Cash Equivalents Items [Line Items]
Available-for-sale debt securities, amortized cost	383	368
Available-for-sale debt securities	383	367
Long-term investments
Cash and Cash Equivalents Items [Line Items]
Available-for-sale debt securities, amortized cost	13	13
Available-for-sale debt securities	$ 13	$ 13