Percentage of exercise price equal to market price on the date of grant.

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Percentage of vesting in first anniversary.

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Percentage of vesting in second anniversary.

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Percentage of vesting in third anniversary.

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Supplemental retirement savings plan aggregate value of the accounts, shares.

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Amount, after tax, of expense for award under share-based payment arrangement.

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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 cash inflow 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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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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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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The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Intrinsic value of vested award under share-based payment arrangement. Excludes share and unit options.

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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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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020	Mar. 11, 2021
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of vesting in first anniversary	30.00%
Percentage of vesting in second anniversary	30.00%
Percentage of vesting in third anniversary	40.00%
Net stock-based compensation expense	$ 22	$ 20	$ 9
Stock Options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of exercise price equal to market price on the date of grant	100.00%
Vesting period (in years)	3 years
Expiration period, years	10 years
Unrecognized compensation cost	$ 3
Weighted-average period, years	1 year
Options outstanding, aggregate intrinsic value	$ 22
Options exercisable, aggregate intrinsic value	22
Intrinsic value of options exercised	4	2
Cash received from exercises	$ 6	$ 5	$ 1
Stock Options, Weighted Average Grant Date Fair Value, Granted	$ 15.95	$ 9.69	$ 10.68
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period (in years)	3 years
Unrecognized compensation cost	$ 24
Weighted-average period, years	1 year
Estimated weighted average grant date fair value	$ 58.72	$ 41.92	$ 49.36
Intrinsic value of restricted stock units vested	$ 13	$ 8	$ 13
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period (in years)	3 years
2017 Long-Term Incentive Plan [Member] \| Maximum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, authorized shares				8,625,000
Supplemental 401(k) Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Supplemental retirement savings plan, aggregate value of the accounts, shares	103,000	77,000