Cash and Cash Equivalents, Investments, and Funds Held for Customers - Table of cash and cash equivalents, investments, and funds held for customers by investment type (Details) - USD ($) $ in Millions	12 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2014
Amortized Cost
Total cash and cash equivalents	$ 529	$ 638	$ 808	$ 849
Total cash and cash equivalents, investments, and funds held for customers	1,179	1,411
Fair Value
Total cash and cash equivalents, investments, and funds held for customers	1,180	1,412
Gross realized gains and losses on our available-for-sale debt securities	0	0	$ 0
Gross unrealized gains and losses on our available-for-sale debt securities	0	0
Total cash and cash equivalents
Amortized Cost
Total cash and cash equivalents	701	742
Fair Value
Total cash and cash equivalents	701	742
Municipal bonds
Amortized Cost
Total available-for-sale debt securities	63	186
Fair Value
Total available-for-sale securities	63	186
Municipal auction rate securities
Amortized Cost
Total available-for-sale debt securities	15	15
Fair Value
Total available-for-sale securities	15	15
Corporate notes
Amortized Cost
Total available-for-sale debt securities	381	419
Fair Value
Total available-for-sale securities	382	420
U.S. agency securities
Amortized Cost
Total available-for-sale debt securities	3	36
Fair Value
Total available-for-sale securities	3	36
Total available-for-sale debt securities
Amortized Cost
Total available-for-sale debt securities	462	656
Fair Value
Total available-for-sale securities	463	657
Other long-term investments
Amortized Cost
Other long-term investments	16	13
Fair Value Measurement | Other long-term investments
Amortized Cost
Other long-term investments	$ 16	$ 13