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Equity (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
Equity (Detail) - USD ($) $ in Millions	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Non-cash stock-based compensation expense	$ 9	$ 21	$ 18	$ 35
Income tax obligations	5		5
Restricted Stock Units (RSUs) And Common Stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Non-cash stock-based compensation expense			12
Performance Shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Non-cash stock-based compensation expense	$ 1		3	1
Share-Based Payment Arrangement, Tranche One
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation liability		12		12
Share-Based Payment Arrangement, Tranche Two
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Share-based compensation liability		15		15
Additional Paid-in Capital
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Non-cash stock-based compensation expense		$ 9	$ 15	$ 20
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)	170,669	251,000	177,687	256,000
Common Stock \| Class B Common Stock
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Shares issued under the plan (in shares)			1,335,169