Available-for-Sale Debt Investments and Equity Investments (Summary of Gains and Losses Recognized on Marketable and Non-marketable Equity Securities) (Details) $ in Millions	3 Months Ended
	Oct. 27, 2018 USD ($)
Adjustments to non-marketable equity securities measured using the measurement alternative:
Upward adjustments	$ 10
Downward adjustments, including impairments	(16)
Net downward adjustments	(6)
Net gains and losses recognized during the period on equity investments	8
Less: Net gains and losses recognized on equity investments sold	(12)
Unrealized gains and losses recognized during reporting period on equity securities still held at the reporting date	$ (4)