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Share-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	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 share-based compensation expense	$ 23	$ 18	$ 22
Tax benefits from the exercise of stock options	$ 2	2	1
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	$ 76
Options exercisable, aggregate intrinsic value	76
Intrinsic value of options exercised	17	2	4
Cash received from exercises	20	$ 4	$ 6
Tax benefits from the exercise of stock options	$ 2
Stock Options, Weighted Average Grant Date Fair Value, Granted	$ 27.42	$ 26.28	$ 15.95
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period (in years)	3 years
Unrecognized compensation cost	$ 22
Weighted-average period, years	1 year
Estimated weighted average grant date fair value	$ 75.98	$ 73.68	$ 58.72
Intrinsic value of restricted stock units vested	$ 37	$ 20	$ 13
Restricted Stock [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period (in years)	3 years
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	117,000	113,000
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