Cash and Cash Equivalents, Investments, and Funds Held for Customers - Classified by the stated maturity date (Details) - USD ($) $ in Millions	Apr. 30, 2018	Jul. 31, 2017
Amortized Cost
Due within one year	$ 243	$ 209
Due within two years	121	164
Due within three years	68	59
Due after three years	33	30
Total available-for-sale debt securities	465	462
Fair Value
Due within one year	242	209
Due within two years	120	164
Due within three years	67	60
Due after three years	33	30
Total available-for-sale debt securities	$ 462	$ 463