Equity - Narrative (Details) $ / shares in Units, $ in Millions			1 Months Ended	12 Months Ended
	Dec. 01, 2025 USD ($)	Aug. 05, 2025 USD ($) installment $ / shares shares	Oct. 31, 2025 shares	Sep. 30, 2025 USD ($) $ / shares shares	Sep. 30, 2024 USD ($) $ / shares shares	Sep. 30, 2023 USD ($) $ / shares shares	Nov. 14, 2024 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Income tax obligations				$ 20	$ 5	$ 0
Fair value of stock options granted (in dollars per share) | $ / shares				$ 27.48
Fair value of stock options (in dollars per share) | $ / shares				$ 8.48
Non-cash compensation expense				$ 54	52	49
Non-cash stock-based compensation expense				54	$ 52	$ 49
Carrying amount of noncontrolling interest		$ 106
Difference between consideration and the carrying amount of noncontrolling interest		46
Deferred tax assets, noncontrolling interest				$ 13
Redemption of noncontrolling interests, noncash financing activities		134
Stock issued		43
Future stock issuance		81
Share based liability		12
Redeemable noncontrolling interests expenditures incurred but not yet paid		$ 10
Omnibus Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share repurchase authorized, amount							$ 100
10K Projects
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of voting interests acquired (as a percent)		49.00%
Final purchase price		$ 165
Share issued value		$ 112
10K Projects | Business Combination, First Installment
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of installments | installment		2
Purchase price of selected assets		$ 40
Issuance of shares (in shares) | shares		1,416,666
Share issued value		$ 43
Price per share (in dollars per share) | $ / shares		$ 30
10K Projects | Business Combination, First Installment, Payment One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price of selected assets		$ 30
10K Projects | Business Combination, First Installment, Payment Two | Forecast
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price of selected assets	$ 10
10K Projects | Business Combination, Second Installment
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of installments | installment		2
Share issued value		$ 70
Contingent consideration		$ 13
10K Projects | Business Combination, Second Installment, Payment One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of shares (in shares) | shares		2,333,333
Share issued value		$ 70
Price per share (in dollars per share) | $ / shares		$ 30
10K Projects | Business Combination, Second Installment, Payment Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Price per share (in dollars per share) | $ / shares		$ 30
Contingent consideration		$ 13
Contingent consideration payable (in shares) | shares		416,667
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share) | $ / shares				$ 30.73	$ 35.79	$ 34.93
Awards vested in period, intrinsic value				$ 45	$ 4	$ 1
Unrecognized compensation costs				$ 56
Total compensation of unvested awards expected to be recognized, weighted average period				2 years 10 months 24 days
Deferment period				30 days
Vested (in shares) | shares				1,442,026
Non-cash stock-based compensation expense				$ 5	0	13
Restricted Stock Units (RSUs) | Restructuring Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Non-cash stock-based compensation expense				$ 4	$ 14	$ 2
Performance Shares Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in dollars per share) | $ / shares				$ 0	$ 43.49	$ 60.25
Unrecognized compensation costs				$ 5
Total compensation of unvested awards expected to be recognized, weighted average period				1 year
Vested (in shares) | shares				0
Non-cash stock-based compensation expense				$ 11	$ 8	$ 4
Performance Shares Units (PSUs) | Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vested (in shares) | shares			254,731
Stock Option
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation costs				$ 4
Total compensation of unvested awards expected to be recognized, weighted average period				3 years 8 months 12 days
Class A Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under Omnibus incentive plan (in shares) | shares				799,748	206,298	276,516
Class A Common Stock | Omnibus Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share repurchase 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) | shares					206,000	277,000
Shares issued under the plan (in shares) | shares				2,607,027	1,738,016	869,000
Class A Common Stock | Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under Omnibus incentive plan (in shares) | shares			90,588
Class B Common Stock | Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under the plan (in shares) | 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) | shares				31,169,099
Share awards vesting period				10 years
Shares held in employee stock option plan, allocated (in shares) | shares				1,812,081
Common stock available for issuance (in shares) | shares				29,357,018