Cash and Cash Equivalents, Investments, and Funds Held for Customers - Table of cash and cash equivalents, investments, and funds held for customers by balance sheet classification (Details) - USD ($) $ in Millions	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015
Amortized Cost
Cash and cash equivalents	$ 1,464	$ 529	$ 638	$ 808
Investments	454	462
Total cash and cash equivalents, investments, and funds held for customers	2,098	1,179
Fair Value
Investments	452	463
Total cash and cash equivalents, investments, and funds held for customers	2,096	1,180
Cash and cash equivalents
Amortized Cost
Cash and cash equivalents	1,464	529
Fair Value
Cash and cash equivalents	1,464	529
Investments
Amortized Cost
Investments	253	247
Fair Value
Investments	252	248
Funds held for customers
Amortized Cost
Investments	368	372
Fair Value
Investments	367	372
Long-term investments
Amortized Cost
Investments	13	31
Fair Value
Investments	$ 13	$ 31