Cash and Cash Equivalents, Investments, and Funds Held for Customers - Table of available-for-sale debt securities classified by maturity date (Details) - USD ($) $ in Millions	Jul. 31, 2018	Jul. 31, 2017
Amortized Cost
Due within one year	$ 250	$ 209
Due within two years	117	164
Due within three years	66	59
Due after three years	21	30
Total available-for-sale debt securities	454	462
Fair Value
Due within one year	250	209
Due within two years	116	164
Due within three years	65	60
Due after three years	21	30
Total available-for-sale debt securities	$ 452	$ 463