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, 2017	Jul. 31, 2016
Amortized Cost
Due within one year	$ 209	$ 285
Due within two years	164	209
Due within three years	59	143
Due after three years	30	19
Total available-for-sale debt securities	462	656
Fair Value
Due within one year	209	285
Due within two years	164	210
Due within three years	60	143
Due after three years	30	19
Total available-for-sale debt securities	$ 463	$ 657