Leases - Supplemental Cash Flows (Details) - USD ($) $ in Millions	6 Months Ended
	Jan. 31, 2021	Jan. 31, 2020
Leases [Abstract]
Cash paid for amounts included in the measurement of operating lease liabilities	$ 31	$ 33
Right-of-use assets obtained in exchange for new operating lease liabilities	27	328
Right-of-use assets, obtained in exchange for new operating lease liabilities, existing prior to August 1, 2019		$ 319
Right-of-use assets, obtained in exchange for new operating lease liabilities, operating leases not yet commenced	$ 9