Share-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Employee Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration period of options issued under EIP	10 years
Vesting period from the date of grant	3 years
Total intrinsic value from options exercised	$ 107	$ 249	$ 178
Tax benefit from exercise of stock options	23	55	62
Unrecognized compensation cost	$ 19
Total unrecognized compensation cost related to non-vested options expected to be recognized over a weighted average period (in years)	6 months
Weighted average remaining contractual term	6 years 9 months 29 days
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period from the date of grant	3 years
Total fair value of RSAs and RSUs vested	$ 228	$ 183	$ 163
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost	$ 332
Weighted average grant date fair value of RSUs (in dollars per share)	$ 137.38	$ 111.11	$ 81.67
Weighted average remaining contractual term	25 days
Performance-based Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period from the date of grant	3 years	3 years	3 years
Unrecognized compensation cost	$ 37
Weighted average grant date fair value of RSUs (in dollars per share)	$ 153.42	$ 120.11	$ 86.37
Weighted average remaining contractual term	24 days
2007 Equity Incentive Compensation Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of Class A Common Stock authorized for issuance under EIP or ESPP (in shares)	236,000,000
Share-based compensation expense under EIP	$ 388	$ 312	$ 224
Tax benefit under EIP	$ 59	$ 53	$ 67
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of Class A Common Stock authorized for issuance under EIP or ESPP (in shares)	20,000,000
ESPP discount from market price	15.00%

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Amount of tax benefit from exercise of option under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Discount rate from fair value on purchase date that participants pay for shares.

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Number of shares authorized for issuance under share-based payment arrangement.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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