Property and Equipment - Schedule of property and equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Jul. 31, 2018	Jul. 31, 2017
Property, Plant and Equipment [Line Items]
Equipment	$ 479	$ 579
Computer software	812	749
Furniture and fixtures	88	82
Leasehold improvements	325	310
Land	79	81
Buildings	363	547
Capital in progress	48	71
Total property plant and equipment, gross	2,194	2,419
Less accumulated depreciation and amortization	(1,382)	(1,389)
Total property and equipment, net	$ 812	$ 1,030
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)	2 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)	3 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