Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2022	Nov. 14, 2024
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Income tax obligations	$ 5	$ 0	$ 6
Non-cash compensation expense	52	49	39
Non-cash stock-based compensation expense	$ 52	$ 49	$ 39
Omnibus Incentive Plan | Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share repurchase program, authorized, amount				$ 100
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 35.79	$ 34.93	$ 44.38
Awards vested in period, intrinsic value	$ 4	$ 1	$ 18
Unrecognized compensation costs	$ 37
Total compensation of unvested awards expected to be recognized, weighted average period	2 years 8 months 12 days
Non-cash stock-based compensation expense	$ 13
Restricted Stock Units (RSUs) | Restructuring Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-cash stock-based compensation expense	$ 14	$ 2
Performance Shares Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share)	$ 43.49	$ 60.25
Unrecognized compensation costs	$ 16
Total compensation of unvested awards expected to be recognized, weighted average period	1 year 7 months 6 days
Non-cash stock-based compensation expense	$ 8	$ 4
Class A Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under Omnibus incentive plan (in shares)	206,298	276,516	463,826
Class A Common Stock | Omnibus Incentive Plan | Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share repurchase program, authorized, amount				$ 100
Class A Common Stock | Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under Omnibus incentive plan (in shares)	206,000	277,000	187,000
Shares issued under the plan (in shares)	1,738,016	869,008
Common Class B | Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under the plan (in shares)	2,270,136
Omnibus Incentive Plan | Class A Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation arrangement by share-based payment award, number of shares available for grant (in shares)	31,169,099
Share awards vesting period	10 years
Shares held in employee stock option plan, allocated (in shares)	1,011,333
Common stock available for issuance (in shares)	30,157,766