Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021	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	$ 18	$ 22	$ 20
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	$ 29
Options exercisable, aggregate intrinsic value	29
Intrinsic value of options exercised	2	4	2
Cash received from exercises	$ 4	$ 6	$ 5
Stock Options, Weighted Average Grant Date Fair Value, Granted	$ 26.28	$ 15.95	$ 9.69
Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period (in years)	3 years
Unrecognized compensation cost	$ 16
Weighted-average period, years	1 year
Estimated weighted average grant date fair value	$ 73.68	$ 58.72	$ 41.92
Intrinsic value of restricted stock units vested	$ 20	$ 13	$ 8
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	113,000	103,000
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