Cash and Cash Equivalents, Investments, and Funds Held for Customers - Type of issue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017	Jul. 31, 2017	Jul. 31, 2016
Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents, amortized cost	$ 478	$ 392	$ 478	$ 392	$ 529	$ 638
Available-for-sale securities:
Total cash and cash equivalents, investments, and funds held for customers, Amortized Cost	1,178		1,178		1,179
Total cash and cash equivalents, investments, and funds held for customers, Fair Value	1,176		1,176		1,180
Available-for-sale Securities, Gross Realized Gain (Loss)	0	$ 0	0	0
Debt Securities, Available-for-sale, Unrealized Gain (Loss)			0	$ 0
Total cash and cash equivalents
Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalents, amortized cost	700		700		701
Cash and cash equivalents, fair value	700		700		701
Municipal bonds
Available-for-sale securities:
Investments and funds, amortized cost	51		51		63
Investments and funds, fair value	50		50		63
Corporate notes
Available-for-sale securities:
Investments and funds, amortized cost	389		389		381
Investments and funds, fair value	388		388		382
U.S. agency securities
Available-for-sale securities:
Investments and funds, amortized cost	10		10		3
Investments and funds, fair value	10		10		3
Municipal auction rate securities
Available-for-sale securities:
Investments and funds, amortized cost	15		15		15
Investments and funds, fair value	15		15		15
Total available-for-sale debt securities
Available-for-sale securities:
Investments and funds, amortized cost	465		465		462
Investments and funds, fair value	463		463		463
Other long-term investments
Available-for-sale securities:
Other long-term investments, amortized cost	13		13		16
Investments and funds, fair value	$ 13		$ 13		$ 16