Stockholders' Equity - Additional Information (Details)		12 Months Ended
	Jan. 19, 2017 shares	Jul. 31, 2018 USD ($) Period_of_time $ / shares shares	Jul. 31, 2017 USD ($) $ / shares shares	Jul. 31, 2016 USD ($) $ / shares shares	Aug. 31, 2018 $ / shares	Aug. 21, 2018 USD ($)	Jul. 31, 2015 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cash dividends declared per common share (in dollars per share) | $ / shares		$ 1.56	$ 1.36	$ 1.20
Stock repurchased during period (in shares)		$ 272,000,000	$ 839,000,000	$ 2,264,000,000
Common stock dividends, cash paid (in dollars per share) | $ / shares		$ 1.56
Dividends and dividend rights paid		$ 407,000,000	$ 353,000,000	$ 318,000,000
Additional shares authorized (in shares) | shares			23,110,000
Common stock, shares authorized (in shares) | shares		750,000,000	750,000,000
Pool shares reduced for each share granted (in shares) | shares		2.3
Pool shares increased for each share forfeited (in shares) | shares		2.3
Shares available for grant (in shares) | shares		22,791,000	25,164,000	8,990,000			17,183,000
Stock offering period, months, employee stock purchase plans		6 months
Stock accrual period, employee stock purchase plans, number of accrual periods | Period_of_time		2
Stock offering period, number of months in accrual period		3 months
Percentage of lower of the closing price for stock on the first day last day of the offering period		85.00%
Shares issued during period for Employee Stock Purchase Plans (in shares) | shares		612,768	752,605	882,206
Shares available for issuance under Employee Stock Purchase Plan (in shares) | shares		2,391,194
Excess tax benefits related to stock-based compensation		$ 100,000,000	$ 72,000,000
Net cash provided by operating activities		2,112,000,000	1,599,000,000	$ 1,460,000,000
Net cash used in financing activities		634,000,000	1,632,000,000	1,999,000,000
Deferred tax assets		$ 87,000,000	$ 132,000,000
Cumulative effect of change in accounting principle				$ 2,000,000
Restated 2005 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized (in shares) | shares	23,100,000
Common stock, shares authorized (in shares) | shares		138,100,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for grant (in shares) | shares		22,800,000
Number of years until options vest		7 years
Stock Options | Restated 2005 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pool shares reduced for each share granted (in shares) | shares		1
Number of shares added back to plan when grants are forfeited (in shares) | shares		1
Employee Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, shares authorized (in shares) | shares		23,800,000
Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend per share payable (in dollars per share) | $ / shares					$ 0.47
Current Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchase program remaining authorized repurchase amount		$ 1,200,000,000
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchases under stock repurchase programs (in shares) | shares		1,870,000	6,900,000	24,816,000
Common Stock | Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchase program, additional authorized amount						$ 2,000,000,000
Total authorized amount						$ 3,200,000,000
Additional Paid-In Capital
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative effect of change in accounting principle				$ 6,000,000
Retained Earnings
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative effect of change in accounting principle				(4,000,000)
Minimum | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)		3 years
Minimum | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)		3 years
Maximum | Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)		4 years
Maximum | Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)		4 years
Accounting Standards Update 2016-09
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Excess tax benefits related to stock-based compensation		$ 100,000,000	$ 72,000,000
Net cash provided by operating activities				59,000,000
Net cash used in financing activities				59,000,000
Deferred tax assets				2,000,000
Accounting Standards Update 2016-09 | Additional Paid-In Capital
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative effect of change in accounting principle				6,000,000
Accounting Standards Update 2016-09 | Retained Earnings
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Cumulative effect of change in accounting principle				$ 4,000,000