Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Total net revenue	$ 842	$ 2,541	$ 1,016	$ 778	$ 754	$ 2,304	$ 923	$ 713	$ 5,177	$ 4,694	$ 4,192
Cost of revenue	183	237	206	183	171	216	199	166
All other costs and expenses	669	860	788	656	639	803	682	576
Operating income from continuing operations	(10)	1,444	22	(61)	(56)	1,285	42	(29)	1,395	1,242	738
Net income (loss) from continuing operations					(40)	848	29	(31)	971	806	413
Net income (loss) from discontinued operations					0	178	(5)	0	0	173	(48)
Net income	$ 24	$ 964	$ 13	$ (30)	$ (40)	$ 1,026	$ 24	$ (31)	$ 971	$ 979	$ 365
Basic net income (loss) per share from continuing operations (in dollars per share)					$ (0.16)	$ 3.30	$ 0.11	$ (0.11)	$ 3.78	$ 3.08	$ 1.47
Basic net income (loss) per share from discontinued operations (in dollars per share)					0	0.70	(0.02)	0	0	0.65	(0.17)
Basic net income per share (in dollars per share)	$ 0.09	$ 3.76	$ 0.05	$ (0.12)	(0.16)	4.00	0.09	(0.11)	3.78	3.73	1.30
Diluted net income (loss) per share from continuing operations (in dollars per share)					(0.16)	3.26	0.11	(0.11)	3.72	3.04	1.45
Diluted net income (loss) per share from discontinued operations (in dollars per share)					0	0.68	(0.02)	0	0	0.65	(0.17)
Diluted net income per share (in dollars per share)	$ 0.09	$ 3.70	$ 0.05	$ (0.12)	$ (0.16)	$ 3.94	$ 0.09	$ (0.11)	$ 3.72	$ 3.69	$ 1.28