Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016	Jul. 31, 2016
Income Tax Disclosure [Abstract]
Excess tax benefit recognized	$ 7		$ 26
Discrete tax benefit due to changes In federal tax law		$ 12
Effective tax rate			72.00%	87.00%
Effective income tax rate reconciliation, excluding discrete tax benefits, percent	34.00%	35.00%	34.00%	35.00%
Federal statutory income tax rate	35.00%	35.00%	35.00%	35.00%
Income tax benefit	$ 3	$ 1	$ 45	$ 10
Income before income taxes	$ 10	$ 28	$ (62)	$ (12)
Total amount of unrecognized tax benefits					$ 60
Unrecognized tax benefits, net of related deferred tax assets					40
Favorable net impact to income tax expense due to recognition of tax benefits					$ 40