Property and Equipment - Schedule of property and equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Jul. 31, 2017	Jul. 31, 2016
Property, Plant and Equipment [Line Items]
Equipment	$ 579	$ 533
Computer software	749	619
Furniture and fixtures	82	73
Leasehold improvements	310	296
Land	81	60
Buildings	547	403
Capital in progress	71	256
Total property plant and equipment, gross	2,419	2,240
Less accumulated depreciation and amortization	(1,389)	(1,209)
Total property and equipment, net	$ 1,030	$ 1,031
Minimum
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life (in years)	2 years
Maximum
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life (in years)	30 years
Equipment | Minimum
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life (in years)	3 years
Equipment | Maximum
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life (in years)	5 years
Computer software | Minimum
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life (in years)	3 years
Computer software | Maximum
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life (in years)	6 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life (in years)	5 years
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life (in years)	2 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life (in years)	16 years
Buildings | Minimum
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life (in years)	5 years
Buildings | Maximum
Property, Plant and Equipment [Line Items]
Property and Equipment, Useful Life (in years)	30 years