Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2016	Jan. 31, 2015	Jul. 31, 2015
Income Tax Disclosure [Abstract]
Tax benefit for research credits	$ 12
Income tax benefit	1	$ 34	$ 10	$ 69
Income (loss) before income taxes	$ 28	$ (94)	$ (12)	$ (210)
Effective tax rate		37.00%	87.00%	33.00%
Effective income tax rate reconciliation, excluding discrete tax benefits, percent	35.00%	36.00%	35.00%	36.00%
Federal statutory income tax rate	35.00%	35.00%	35.00%	35.00%
Total amount of unrecognized tax benefits					$ 56
Unrecognized tax benefits, net of related deferred tax assets					37
Favorable net impact to income tax expense due to recognition of tax benefits					$ 37