Equity - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Non-cash stock-based compensation expense	$ 9	$ 14
Share-Based Payment Arrangement, Tranche Two
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation liability		10
Additional Paid-in Capital
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Non-cash stock-based compensation expense	$ 15	$ 4
Common Stock \| Class A Common Stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares issued under the plan (in shares)	1,738,016	869,000
Shares issued under omnibus incentive plan (in shares)	7,000	5,000
Common Stock \| Class B Common Stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares issued under the plan (in shares)	547,249

Carrying value as of the balance sheet date of obligations, excluding pension and other postretirement benefits, incurred through that date and payable for perquisites provided to employees pertaining to services received from them.

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